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Structure and Function of the Thin Limbs of the Loop of Henle

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Abstract

The thin limbs of the loop of Henle, which comprise the intermediate segment, connect the proximal tubule to the distal tubule and lie entirely within the renal medulla. The descending thin limb consists of at least two or three morphologically and functionally distinct subsegments and participates in transepithelial transport of NaCl, urea, and water. Only one functionally distinct segment is recognized for the ascending thin limb, which carries out transepithelial transport of NaCl and urea in the reabsorptive and/or secretory directions. Membrane transporters involved with passive transcellular Cl, urea, and water fluxes have been characterized for thin limbs; however, these pathways do not account for all transepithelial fluid and solute fluxes that have been measured in vivo. The paracellular pathway has been proposed to play an important role in transepithelial Na and urea fluxes in defined thin‐limb subsegments. As the transport pathways become clearer, the overall function of the thin limbs is becoming better understood. Primary and secondary signaling pathways and protein‐protein interactions are increasingly recognized as important modulators of thin‐limb cell function and cell metabolism. These functions must be investigated under diverse extracellular conditions, particularly for those cells of the deep inner medulla that function in an environment of wide variation in hyperosmolality. Transgenic mouse models of several key water and solute transport proteins have provided significant insights into thin‐limb function. An understanding of the overall architecture of the medulla, including juxtapositions of thin limbs with collecting ducts, thick ascending limbs, and vasa recta, is essential for understanding the role of the kidney in maintaining Na and water homeostasis, and for understanding the urine concentrating mechanism. © 2012 American Physiological Society. Compr Physiol 2:2063‐2086, 2012.

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Figure 1. Figure 1.

Segmentation of thin limbs of the loop of Henle. The short‐loop nephron (right, belonging to a superficial glomerulus) has a descending thick limb (pars recta of proximal tubule; hatched), a descending thin limb (DTL) (turning back near the outer medullary‐inner medullary boundary), and a thick ascending limb (cross hatched), which passes into the distal convoluted tubule a short distance beyond the macula densa (shown in black). The long‐loop nephron (second from right, belonging to a juxtamedullary glomerulus) contains a DTL subdivided into two parts, type 2 and type 3 epithelium; and an ascending thin limb (ATL), type 4 epithelium; the bend is located in the inner medulla. Two additional long‐loop nephrons (incompletely drawn) demonstrate heterogeneity among long‐loop nephrons, which turn back at different levels within the inner medulla. Numbers 1‐4 refer to type of epithelium encountered in corresponding thin limb part: type 1, DTL of short loops; type 2, upper part of DTL of long loops; type 3, lower part of DTL of long loops; type 4 (beginning short distance before bend), ATL. Aquaporin 1 (AQP1)‐negative segments/yellow; AQP1‐positive segments/red; ClC‐K1‐positive segments/green. Figure based on data adapted, with permission, from references , and .

Figure 2. Figure 2.

Segmentation of C57/BL/6J mouse short‐loop and long‐loop nephrons. Tortuous descending thin limb (DTL) of long‐loop nephron (LLN; large arrow); winding course of thick ascending limb (red arrowhead) of short‐loop nephron (SLN) and CD (black arrowhead); a piece of TAL inserted in the DTL of LLN (LLNt; small arrow), which forms its bend just beneath the “transitional zone” within the inner medulla; and three different types of SLN bends (SLN1, SLN2, and SLN3). Outer stripe of outer medulla (OSOM), inner stripe of outer medulla (ISOM), and inner medulla (IM). Figure adapted, with permission, from reference .

Figure 3. Figure 3.

Immunolocalization of wide‐bend thin limbs of loops of Henle (arrows), ascending thin limb (ATLs), and CDs in Munich‐Wistar rat papilla. ATLs and wide‐bend loops/ClC‐K1/green (structure/immunogen/color), and CDs/aquaporin 2 (AQP2)/blue in a transverse section that lies 70 μm above the tip of the papilla. Scale bar, 100 μm. Figure adapted, with permission, from reference .

Figure 4. Figure 4.

Type 1 epithelium of rat short‐loop descending thin limb (DTL). (A) Overview of cross‐sectional profile, x ∼ 4000. (B) Simple type 1 epithelium, x ∼ 12,000. (C) Complex tight junction in freeze‐fracture replica, x ∼ 71000. Intramembrane particle clusters (*) seen on P‐face of basolateral membrane correspond to desmosomes. Figure modified, with permission, from reference .

Figure 5. Figure 5.

Type 2 epithelium of rat long‐loop descending thin limb (DTL) (DTLupper). (A) Overview of tubular profile; note many tight junctions (arrows), x ∼ 4000. (B) Longitudinal section through epithelium; numerous tight junctions (arrows) indicate extensive cellular interdigitation. Note basolateral “labyrinth,” x ∼ 18,000. (C) Flat section through epithelium showing star‐like shape of epithelial cells responsible for cellular interdigitation. Note microfilament bundles (*) in basal epithelium, x ∼ 13,500. Figure modified, with permission, from reference .

Figure 6. Figure 6.

Type 3 epithelium of rat long‐loop descending thin limb (DTL) (DTLlower). (A) Overview of cross‐sectional profile. Only two tight junctions (arrows) are encountered, x ∼ 3750. (B) Simple type 3 epithelium, x ∼ 16,500. (C) Freeze‐fracture electron microscopy shows complex tight junction, x ∼ 52,000. Figure modified, with permission, from reference .

Figure 7. Figure 7.

Type 4 epithelium of rat long‐loop ascending thin limb (ATL). (A) Overview of cross‐sectional profile, x ∼ 3000. Note many tight junctions (arrows). (B) Longitudinal section through epithelium showing high degree of cellular interdigitation (junctions marked by arrows), x ∼ 11,500. (C) Freeze‐fracture electron micrograph showing luminal aspect of two interdigitating cells, x ∼ 12,000. Note two different types of intramembrane textures. Figure modified, with permission, from reference .

Figure 8. Figure 8.

Photomicrographs of Munich‐Wistar rat thin limbs of the loop of Henle from the inner medullary outer zone (OZ; see Fig. ), viewed with differential interference contrast optics. (A) Type 2 epithelium [descending thin limb (DTLupper)] and (B) type 4 epithelium [ascending thin limb (ATL)]. Note cells with nuclei protruding into lumen in type 2 epithelium and cells with large, round, flat nuclei in type 4 epithelium. Scale bar, 100 μm. Figure adapted, with permission, from .

Figure 9. Figure 9.

Immunolocalization of tubules and vessels in the inner stripe of the Munich‐Wistar rat outer medulla. CDs/aquaporin 2 (AQP2)/yellow; long‐loop descending thin limb (DTL)/aquaporin 1 (AQP1)/white; short‐loop DTL/UT‐A2/blue; thick ascending limb/ClC‐K2/orange; descending vasa recta/UT‐B/green. Ascending vasa recta, capillaries, and AQP1‐negative long‐loop DTLs are not shown. Overlay of two adjacent transverse sections, 1 μm apart. Scale bar, 250 μm. Unpublished figure, Thomas Pannabecker.

Figure 10. Figure 10.

Immunolocalization of CDs and associated thin limbs of the loop of Henle in the Munich‐Wistar rat inner medulla. The “intracluster” region is bounded by the red borders, the “intercluster” region lies between the red and white borders. Transverse section is from about 400 μm below the outer medullary‐inner medullary boundary (outer zone 1; see Fig. ). Five primary CD clusters are outlined by white borders; borders were determined by the Euclidean distant map technique (). These five primary clusters make up a single secondary CD cluster that consists of 31 CDs near the outer medullary‐inner medullary boundary. Descending thin limb (DTL)/aquaporin 1 (AQP1)/red, CD/aquaporin 2 (AQP2)/blue, ascending thin limb (ATL)/ClC‐K1/green. Scale bar, 100 μm. Figure modified, with permission, from reference .

Figure 11. Figure 11.

Immunolocalization of thin limbs of the loop of Henle in the Munich‐Wistar rat inner medulla. Transverse sections showing (A) nonuniform distribution of aquaporin 1 (AQP1)‐positive descending thin limb (DTL)/AQP1/red and (B) near uniform distribution of prebend segments and ascending thin limb (ATL)/ClC‐K1/green. Sections lie within 1300 μm below the outer medullary‐inner medullary boundary (outer zone 2, see Fig. ). AQP1‐negative DTLs are not shown. Scale bars, 100 μm. Figure modified, with permission, from reference .

Figure 12. Figure 12.

Three‐dimensional reconstruction of a primary CD cluster and associated tubules and vessels in the Munich‐Wistar rat inner medulla. (A) Descending thin limbs (DTLs) and descending vasa recta that are associated with a primary CD cluster lie at the periphery of or outside of the cluster along the entire axial length of the cluster. Aquaporin 1 (AQP1)‐positive DTLs/AQP1/red; AQP1‐negative DTLs/α‐B crystalline/gray; descending vasa recta/UT‐B/green; CDs/aquaporin 2 (AQP2)/blue. (B) Ascending thin limbs (ATLs) and prebend segments associated with a primary CD cluster lie at the periphery of, outside of, or amongst the CDs along the entire axial length of the cluster. ATLs and prebend segments/ClCK/green; CDs/AQP2/blue. The upper edge of the image is positioned near the outer medullary‐inner medullary boundary. Scale bars, 250 μm; inset scale bars, 500 μm. Figure modified, with permission, from references and .

Figure 13. Figure 13.

Four subsections, or zones, of the rat inner medulla; based on data from the Munich‐Wistar rat (): (1) an outer‐most zone (OZ1) of about 1 mm thickness, just below the outer medulla, in which loops expressing negligible or no inner medullary aquaporin 1 (AQP‐1) have their bends; (2) a larger outer zone (OZ2), just below the outermost zone, 2 to 2.5 mm in thickness, which contains well‐organized CD clusters in which tubules and vessels are tightly packed and in which loops bend within the central portions of the clusters; (3) an outer inner zone (IZ1) in which the organization of the CD clusters is diminishing and nearly all vasa recta are fenestrated; and (4) an innermost zone (IZ2) in which CD clusters can no longer be distinguished, the CDs appear to dominate all other structures, nearly all vasa recta are fenestrated, and a large fraction of loops have transversely running segments. The two inner zones make up approximately 1.5 to 2 mm of the papilla. CD clusters/blue coalesce into single CDs. AQP1‐positive DTLs/red, AQP1‐negative descending thin limbs (DTLs)/yellow, and ascending thin limbs (ATLs) and prebend segments/green. Scale bar, 1 mm along the axial dimension; lateral dimensions are not to scale. Figure adapted, with permission, from reference .

Figure 14. Figure 14.

Organization of a primary CD cluster and thin limbs of the loop of Henle in the Munich‐Wistar rat inner medulla. (A, B) A single transverse section from near the outer medullary‐inner medullary boundary (outer zone 1; see Fig. ) showing profiles of CDs and associated thin limbs. Aquaporin 1 (AQP1)‐positive descending thin limbs (DTLs)/AQP1/filled red; AQP1‐negative DTLs/α‐B crystallin/unfilled red; ATLs and prebend segments/ClCK/green and white; CDs associated with the primary cluster/aquaporin 2 (AQP2)/dark blue; CDs not associated with the primary cluster are shown in light blue. (A) Thin limbs of short long‐loop nephrons associated with the CD cluster. These thin limbs form their bends within 1 mm below the outer medullary‐inner medullary boundary. AQP1‐negative DTLs lie at the edge of the CD cluster and their connecting prebend segments and ATLs lie in the intracluster region. (B) Thin limbs of long long‐loop nephrons associated with the CD cluster. These thin limbs form their bends between approximately 2 to 3 mm below the outer medullary‐inner medullary boundary. AQP1‐positive DTLs and their connecting ascending thin limbs (ATLs) lie in the intercluster region, distant from CDs. (C‐F) Three‐dimensional reconstruction of primary cluster CDs and associated thin limbs that are shown in A and B. AQP1‐positive/red; AQP1‐negative/yellow; ATLs and prebend segments/green; CDs/blue. The outer medullary‐inner medullary boundary lies near the top edge of the figure. (C) DTLs of nephrons that form their bends within 1 mm below the outer medullary‐inner medullary boundary. (D) DTLs of nephrons that form their bends between approximately 2 to 3 mm below the outer medullary‐inner medullary boundary. (E) ATLs of nephrons that form their bends within 1 mm below the outer medullary‐inner medullary boundary, and (F) ATLs of nephrons that form their bends between approximately 2 to 3 mm below the outer medullary‐inner medullary boundary. Scale bars, 100 μm. Figure modified, with permission, from reference .

Figure 15. Figure 15.

Three‐dimensional reconstruction of Munich‐Wistar rat thin limbs of the loop of Henle that form bends at four different levels below the outer medullary‐inner medullary boundary. (A) Thin limbs that form bends within the first mm below the outer medullary‐inner medullary boundary. Descending thin limbs (DTLs) lack detectable aquaporin 1 (AQP1). ClC‐K1 is expressed continuously along the prebend segment and the ascending thin limb (ATL). (B‐D) Thin limbs that form bends below the first millimeter of the inner medulla. AQP1 is expressed along the initial 40% of each DTL (type 2 epithelium), and is absent from the terminal 60% (type 3 epithelium). ClC‐K1 is expressed continuously along the prebend segment and the ATL. Boxed area is enlarged in E. (E) Enlargement of near‐bend regions of four thin limbs from box in D. ClC‐K1 expression begins, on average, approximately 170 μm before the bend (arrows). AQP1‐positive DTLs/AQP1/red; AQP1‐negative DTLs/α‐B crystallin/gray; ATLs and prebend segments/ClCK/green. Scale bars, (A‐D) 500 μm; (E) 100 μm. Figure modified, with permission, from reference .

Figure 16. Figure 16.

Schematic diagram of Munich‐Wistar rat thin limb of loop of Henle architecture along the corticopapillary axis (). In the outer medulla, vascular bundles can be considered to be the central organizing elements around which DTLS of long‐loop nephrons, TALs, CDs, and capillaries are systematically arranged; in the inner medulla, the CD clusters can be considered to be the central organizing elements. DTLs of nephrons that form their bends within 1 mm below the outer medullary‐inner medullary boundary express no detectable AQP1 in their inner medullary segments and lie near the interface of the intercluster and intracluster regions; their ATLs lie within the intracluster region (cf. Fig. ). Descending thin limbs (DTLs) of loops that form their bends deeper than 1 mm below the outer medullary‐inner medullary boundary pass from the intercluster region into the intracluster region above the prebend segment, and their ascending thin limbs (ATLs) exit into the intercluster region above the equivalent postbend length. ATLs may be positioned either adjacent to or distant from their contiguous DTLs. The depicted symmetry between bundle and cluster regions of the outer medulla and inner medulla, respectively, has not been demonstrated.

Figure 17. Figure 17.

Number of Munich‐Wistar rat thin‐limb subsegments along the inner medullary corticopapillary axis. The plot shows the numbers of aquaporin 1 (AQP1)‐positive and AQP1‐negative descending thin limbs (DTLs) and contiguous ascending thin limbs (ATLs) associated with a single secondary CD cluster at successive transverse levels. Prebend segments were not included in the DTL count, and as a result, the number of ATLs exceeds the number of DTLs. The thin‐limb population declines with increasing depth below the outer medullary‐inner medullary boundary, at the exponential rate defined in previous studies (loop decay rate) (). Inset: DTL and ATL segments for two inner medullary nephrons. AQP1‐positive DTL/red; AQP1‐negative DTL/yellow; prebend and ATL/green. Figure modified, with permission, from reference .

Figure 18. Figure 18.

Interstitial nodal spaces in Munich‐Wistar rat inner medulla, as seen with electron microscopy. Electron micrograph shows a transverse section from outer zone 2 (OZ2; see Fig. ), showing ascending thin limbs (ATLs) and ascending vasa recta (AVR) arranged around a single CD. Interstitial nodal spaces are marked with X. Scale bar, 10 μm. Figure adapted, with permission, from reference .



Figure 1.

Segmentation of thin limbs of the loop of Henle. The short‐loop nephron (right, belonging to a superficial glomerulus) has a descending thick limb (pars recta of proximal tubule; hatched), a descending thin limb (DTL) (turning back near the outer medullary‐inner medullary boundary), and a thick ascending limb (cross hatched), which passes into the distal convoluted tubule a short distance beyond the macula densa (shown in black). The long‐loop nephron (second from right, belonging to a juxtamedullary glomerulus) contains a DTL subdivided into two parts, type 2 and type 3 epithelium; and an ascending thin limb (ATL), type 4 epithelium; the bend is located in the inner medulla. Two additional long‐loop nephrons (incompletely drawn) demonstrate heterogeneity among long‐loop nephrons, which turn back at different levels within the inner medulla. Numbers 1‐4 refer to type of epithelium encountered in corresponding thin limb part: type 1, DTL of short loops; type 2, upper part of DTL of long loops; type 3, lower part of DTL of long loops; type 4 (beginning short distance before bend), ATL. Aquaporin 1 (AQP1)‐negative segments/yellow; AQP1‐positive segments/red; ClC‐K1‐positive segments/green. Figure based on data adapted, with permission, from references , and .



Figure 2.

Segmentation of C57/BL/6J mouse short‐loop and long‐loop nephrons. Tortuous descending thin limb (DTL) of long‐loop nephron (LLN; large arrow); winding course of thick ascending limb (red arrowhead) of short‐loop nephron (SLN) and CD (black arrowhead); a piece of TAL inserted in the DTL of LLN (LLNt; small arrow), which forms its bend just beneath the “transitional zone” within the inner medulla; and three different types of SLN bends (SLN1, SLN2, and SLN3). Outer stripe of outer medulla (OSOM), inner stripe of outer medulla (ISOM), and inner medulla (IM). Figure adapted, with permission, from reference .



Figure 3.

Immunolocalization of wide‐bend thin limbs of loops of Henle (arrows), ascending thin limb (ATLs), and CDs in Munich‐Wistar rat papilla. ATLs and wide‐bend loops/ClC‐K1/green (structure/immunogen/color), and CDs/aquaporin 2 (AQP2)/blue in a transverse section that lies 70 μm above the tip of the papilla. Scale bar, 100 μm. Figure adapted, with permission, from reference .



Figure 4.

Type 1 epithelium of rat short‐loop descending thin limb (DTL). (A) Overview of cross‐sectional profile, x ∼ 4000. (B) Simple type 1 epithelium, x ∼ 12,000. (C) Complex tight junction in freeze‐fracture replica, x ∼ 71000. Intramembrane particle clusters (*) seen on P‐face of basolateral membrane correspond to desmosomes. Figure modified, with permission, from reference .



Figure 5.

Type 2 epithelium of rat long‐loop descending thin limb (DTL) (DTLupper). (A) Overview of tubular profile; note many tight junctions (arrows), x ∼ 4000. (B) Longitudinal section through epithelium; numerous tight junctions (arrows) indicate extensive cellular interdigitation. Note basolateral “labyrinth,” x ∼ 18,000. (C) Flat section through epithelium showing star‐like shape of epithelial cells responsible for cellular interdigitation. Note microfilament bundles (*) in basal epithelium, x ∼ 13,500. Figure modified, with permission, from reference .



Figure 6.

Type 3 epithelium of rat long‐loop descending thin limb (DTL) (DTLlower). (A) Overview of cross‐sectional profile. Only two tight junctions (arrows) are encountered, x ∼ 3750. (B) Simple type 3 epithelium, x ∼ 16,500. (C) Freeze‐fracture electron microscopy shows complex tight junction, x ∼ 52,000. Figure modified, with permission, from reference .



Figure 7.

Type 4 epithelium of rat long‐loop ascending thin limb (ATL). (A) Overview of cross‐sectional profile, x ∼ 3000. Note many tight junctions (arrows). (B) Longitudinal section through epithelium showing high degree of cellular interdigitation (junctions marked by arrows), x ∼ 11,500. (C) Freeze‐fracture electron micrograph showing luminal aspect of two interdigitating cells, x ∼ 12,000. Note two different types of intramembrane textures. Figure modified, with permission, from reference .



Figure 8.

Photomicrographs of Munich‐Wistar rat thin limbs of the loop of Henle from the inner medullary outer zone (OZ; see Fig. ), viewed with differential interference contrast optics. (A) Type 2 epithelium [descending thin limb (DTLupper)] and (B) type 4 epithelium [ascending thin limb (ATL)]. Note cells with nuclei protruding into lumen in type 2 epithelium and cells with large, round, flat nuclei in type 4 epithelium. Scale bar, 100 μm. Figure adapted, with permission, from .



Figure 9.

Immunolocalization of tubules and vessels in the inner stripe of the Munich‐Wistar rat outer medulla. CDs/aquaporin 2 (AQP2)/yellow; long‐loop descending thin limb (DTL)/aquaporin 1 (AQP1)/white; short‐loop DTL/UT‐A2/blue; thick ascending limb/ClC‐K2/orange; descending vasa recta/UT‐B/green. Ascending vasa recta, capillaries, and AQP1‐negative long‐loop DTLs are not shown. Overlay of two adjacent transverse sections, 1 μm apart. Scale bar, 250 μm. Unpublished figure, Thomas Pannabecker.



Figure 10.

Immunolocalization of CDs and associated thin limbs of the loop of Henle in the Munich‐Wistar rat inner medulla. The “intracluster” region is bounded by the red borders, the “intercluster” region lies between the red and white borders. Transverse section is from about 400 μm below the outer medullary‐inner medullary boundary (outer zone 1; see Fig. ). Five primary CD clusters are outlined by white borders; borders were determined by the Euclidean distant map technique (). These five primary clusters make up a single secondary CD cluster that consists of 31 CDs near the outer medullary‐inner medullary boundary. Descending thin limb (DTL)/aquaporin 1 (AQP1)/red, CD/aquaporin 2 (AQP2)/blue, ascending thin limb (ATL)/ClC‐K1/green. Scale bar, 100 μm. Figure modified, with permission, from reference .



Figure 11.

Immunolocalization of thin limbs of the loop of Henle in the Munich‐Wistar rat inner medulla. Transverse sections showing (A) nonuniform distribution of aquaporin 1 (AQP1)‐positive descending thin limb (DTL)/AQP1/red and (B) near uniform distribution of prebend segments and ascending thin limb (ATL)/ClC‐K1/green. Sections lie within 1300 μm below the outer medullary‐inner medullary boundary (outer zone 2, see Fig. ). AQP1‐negative DTLs are not shown. Scale bars, 100 μm. Figure modified, with permission, from reference .



Figure 12.

Three‐dimensional reconstruction of a primary CD cluster and associated tubules and vessels in the Munich‐Wistar rat inner medulla. (A) Descending thin limbs (DTLs) and descending vasa recta that are associated with a primary CD cluster lie at the periphery of or outside of the cluster along the entire axial length of the cluster. Aquaporin 1 (AQP1)‐positive DTLs/AQP1/red; AQP1‐negative DTLs/α‐B crystalline/gray; descending vasa recta/UT‐B/green; CDs/aquaporin 2 (AQP2)/blue. (B) Ascending thin limbs (ATLs) and prebend segments associated with a primary CD cluster lie at the periphery of, outside of, or amongst the CDs along the entire axial length of the cluster. ATLs and prebend segments/ClCK/green; CDs/AQP2/blue. The upper edge of the image is positioned near the outer medullary‐inner medullary boundary. Scale bars, 250 μm; inset scale bars, 500 μm. Figure modified, with permission, from references and .



Figure 13.

Four subsections, or zones, of the rat inner medulla; based on data from the Munich‐Wistar rat (): (1) an outer‐most zone (OZ1) of about 1 mm thickness, just below the outer medulla, in which loops expressing negligible or no inner medullary aquaporin 1 (AQP‐1) have their bends; (2) a larger outer zone (OZ2), just below the outermost zone, 2 to 2.5 mm in thickness, which contains well‐organized CD clusters in which tubules and vessels are tightly packed and in which loops bend within the central portions of the clusters; (3) an outer inner zone (IZ1) in which the organization of the CD clusters is diminishing and nearly all vasa recta are fenestrated; and (4) an innermost zone (IZ2) in which CD clusters can no longer be distinguished, the CDs appear to dominate all other structures, nearly all vasa recta are fenestrated, and a large fraction of loops have transversely running segments. The two inner zones make up approximately 1.5 to 2 mm of the papilla. CD clusters/blue coalesce into single CDs. AQP1‐positive DTLs/red, AQP1‐negative descending thin limbs (DTLs)/yellow, and ascending thin limbs (ATLs) and prebend segments/green. Scale bar, 1 mm along the axial dimension; lateral dimensions are not to scale. Figure adapted, with permission, from reference .



Figure 14.

Organization of a primary CD cluster and thin limbs of the loop of Henle in the Munich‐Wistar rat inner medulla. (A, B) A single transverse section from near the outer medullary‐inner medullary boundary (outer zone 1; see Fig. ) showing profiles of CDs and associated thin limbs. Aquaporin 1 (AQP1)‐positive descending thin limbs (DTLs)/AQP1/filled red; AQP1‐negative DTLs/α‐B crystallin/unfilled red; ATLs and prebend segments/ClCK/green and white; CDs associated with the primary cluster/aquaporin 2 (AQP2)/dark blue; CDs not associated with the primary cluster are shown in light blue. (A) Thin limbs of short long‐loop nephrons associated with the CD cluster. These thin limbs form their bends within 1 mm below the outer medullary‐inner medullary boundary. AQP1‐negative DTLs lie at the edge of the CD cluster and their connecting prebend segments and ATLs lie in the intracluster region. (B) Thin limbs of long long‐loop nephrons associated with the CD cluster. These thin limbs form their bends between approximately 2 to 3 mm below the outer medullary‐inner medullary boundary. AQP1‐positive DTLs and their connecting ascending thin limbs (ATLs) lie in the intercluster region, distant from CDs. (C‐F) Three‐dimensional reconstruction of primary cluster CDs and associated thin limbs that are shown in A and B. AQP1‐positive/red; AQP1‐negative/yellow; ATLs and prebend segments/green; CDs/blue. The outer medullary‐inner medullary boundary lies near the top edge of the figure. (C) DTLs of nephrons that form their bends within 1 mm below the outer medullary‐inner medullary boundary. (D) DTLs of nephrons that form their bends between approximately 2 to 3 mm below the outer medullary‐inner medullary boundary. (E) ATLs of nephrons that form their bends within 1 mm below the outer medullary‐inner medullary boundary, and (F) ATLs of nephrons that form their bends between approximately 2 to 3 mm below the outer medullary‐inner medullary boundary. Scale bars, 100 μm. Figure modified, with permission, from reference .



Figure 15.

Three‐dimensional reconstruction of Munich‐Wistar rat thin limbs of the loop of Henle that form bends at four different levels below the outer medullary‐inner medullary boundary. (A) Thin limbs that form bends within the first mm below the outer medullary‐inner medullary boundary. Descending thin limbs (DTLs) lack detectable aquaporin 1 (AQP1). ClC‐K1 is expressed continuously along the prebend segment and the ascending thin limb (ATL). (B‐D) Thin limbs that form bends below the first millimeter of the inner medulla. AQP1 is expressed along the initial 40% of each DTL (type 2 epithelium), and is absent from the terminal 60% (type 3 epithelium). ClC‐K1 is expressed continuously along the prebend segment and the ATL. Boxed area is enlarged in E. (E) Enlargement of near‐bend regions of four thin limbs from box in D. ClC‐K1 expression begins, on average, approximately 170 μm before the bend (arrows). AQP1‐positive DTLs/AQP1/red; AQP1‐negative DTLs/α‐B crystallin/gray; ATLs and prebend segments/ClCK/green. Scale bars, (A‐D) 500 μm; (E) 100 μm. Figure modified, with permission, from reference .



Figure 16.

Schematic diagram of Munich‐Wistar rat thin limb of loop of Henle architecture along the corticopapillary axis (). In the outer medulla, vascular bundles can be considered to be the central organizing elements around which DTLS of long‐loop nephrons, TALs, CDs, and capillaries are systematically arranged; in the inner medulla, the CD clusters can be considered to be the central organizing elements. DTLs of nephrons that form their bends within 1 mm below the outer medullary‐inner medullary boundary express no detectable AQP1 in their inner medullary segments and lie near the interface of the intercluster and intracluster regions; their ATLs lie within the intracluster region (cf. Fig. ). Descending thin limbs (DTLs) of loops that form their bends deeper than 1 mm below the outer medullary‐inner medullary boundary pass from the intercluster region into the intracluster region above the prebend segment, and their ascending thin limbs (ATLs) exit into the intercluster region above the equivalent postbend length. ATLs may be positioned either adjacent to or distant from their contiguous DTLs. The depicted symmetry between bundle and cluster regions of the outer medulla and inner medulla, respectively, has not been demonstrated.



Figure 17.

Number of Munich‐Wistar rat thin‐limb subsegments along the inner medullary corticopapillary axis. The plot shows the numbers of aquaporin 1 (AQP1)‐positive and AQP1‐negative descending thin limbs (DTLs) and contiguous ascending thin limbs (ATLs) associated with a single secondary CD cluster at successive transverse levels. Prebend segments were not included in the DTL count, and as a result, the number of ATLs exceeds the number of DTLs. The thin‐limb population declines with increasing depth below the outer medullary‐inner medullary boundary, at the exponential rate defined in previous studies (loop decay rate) (). Inset: DTL and ATL segments for two inner medullary nephrons. AQP1‐positive DTL/red; AQP1‐negative DTL/yellow; prebend and ATL/green. Figure modified, with permission, from reference .



Figure 18.

Interstitial nodal spaces in Munich‐Wistar rat inner medulla, as seen with electron microscopy. Electron micrograph shows a transverse section from outer zone 2 (OZ2; see Fig. ), showing ascending thin limbs (ATLs) and ascending vasa recta (AVR) arranged around a single CD. Interstitial nodal spaces are marked with X. Scale bar, 10 μm. Figure adapted, with permission, from reference .

References
 1. Akizuki N, Uchida S, Sasaki S, Marumo F. Impaired solute accumulation in inner medulla of Clcnk1‐/‐ mice kidney. Am J Physiol Renal Physiol 280: F79‐F87, 2001.
 2. Alper SL, Stuart‐Tilley AK, Biemesderfer D, Shmukler BE, Brown D. Immunolocalization of AE2 anion exchanger in rat kidney. Am J Physiol Renal Physiol 273: F601‐F614, 1997.
 3. Angelow S, Ahlstrom R, Yu ASL. Biology of claudins. Am J Physiol Renal Physiol 295: F867‐F876, 2008.
 4. Angelow S, El‐Husseini R, Kanzawa SA, Yu ASL. Renal localization and function of the tight junction protein, claudin‐19. Am J Physiol Renal Physiol 293: F166‐F177, 2007.
 5. Bachmann S, Kriz W. Histotopography and ultrastructure of the thin limbs of the loop of Henle in the hamster. Cell Tissue Res 225: 111‐127, 1982.
 6. Bagnasco S, Balaban R, Fales HM, Yang Y‐M, Burg M. Predominant osmotically active organic solutes in rat and rabbit renal medullas. J Biol Chem 261: 5872‐5877, 1986.
 7. Bailey MA, Haton C, Orea V, Sassard J, Bailly C, Unwin RJ, Imbert‐Teboul M. ETA receptor‐mediated Ca2+ signaling in thin descending limbs of Henle's loop: Impairment in genetic hypertension. Kidney Int 63: 1276‐1284, 2003.
 8. Bankir L, De Rouffignac C. Urinary concentrating ability: Insights from comparative anatomy. Am J Physiol 249: R643‐R666, 1985.
 9. Barlassina C, Dal Fiume C, Lanzani C, Manunta P, Guffanti G, Ruello A, Bianchi G, Del Vecchio L, Macciardi F, Cusi D. Common genetic variants and haplotypes in renal CLCNKA gene are associated to salt‐sensitive hypertension. Hum Mol Genet 16: 1630‐1638, 2007.
 10. Barrett JM, Kriz W, Kaissling B, De Rouffignac C. The ultrastructure of the nephrons of the desert rodent (Psammonys obesus) kidney. II. Thin limbs of Henle of long‐looped nephrons. Am J Anat 151: 499‐514, 1978.
 11. Bergler T, Stoelcker B, Jeblick R, Reinhold SW, Wolf K, Riegger GAJ, Kramer BK. High osmolality induces the kidney‐specific chloride channel CLC‐K1 by a serum and glucocorticoid‐inducible kinase 1 MAPK pathway. Kidney Int 74: 1170‐1177, 2008.
 12. Beuchat CA. Structure and concentrating ability of the mammalian kidney: Correlations with habitat. Am J Physiol Regul Integr Comp Physiol 271: R157‐R179, 1996.
 13. Biemesderfer D, Rutherford PA, Nagy T, Pizzonia JH, Abu‐Alfa AK, Aronson PS. Monoclonal antibodies for high‐resolution localization of NHE3 in adult and neonatal rat kidney. Am J Physiol Renal Physiol 273: F289‐F299, 1997.
 14. Birkenhager R, Otto E, Schurmann MJ, Vollmer M, Ruf EM, Maier‐Lutz I, Beekmann F, Fekete A, Omran H, Feldmann D, Milford DV, Jeck N, Konrad M, Landau D, Knoers NVAM, Antignac C, Sudbrak R, Kispert A, Hildebrandt F. Mutation of BSND causes Bartter syndrome with sensorineural deafness and kidney failure. Nat Genet 29: 310‐314, 2001.
 15. Braun EJ, Dantzler WH. Vertebrate renal system. In: Handbook of Physiology: Comparative Physiology, Vol. 1. 1997. American Physiological Society; Oxford University Press, NY.
 16. Brokl OH, Dantzler WH. Amino acid fluxes in rat thin limb segments of Henle's loop during in vitro microperfusion. Am J Physiol 277: F204‐F210, 1999.
 17. Brown D, Hirsch S, Gluck S. Localization of a proton‐pumping ATPase in rat‐kidney. J Clin Invest 82: 2114‐2126, 1988.
 18. Brown D, Kumpulainen T, Roth J, Orci L. Immunohistochemical localization of carbonic‐anhydrase in postnatal and adult‐rat kidney. Am J Physiol 245: F110‐F118, 1983.
 19. Bruzzi I, Corna D, Zoja C, Orisio S, Schiffrin EL, Cavallotti D, Remuzzi G, Benigni A. Time course and localization of endothelin‐1 gene expression in a model of renal disease progression. Am J Pathol 151: 1241‐1247, 1997.
 20. Carrithers SL, Taylor B, Cai WY, Johnson BR, Ott CE, Greenberg RN, Jackson BA. Guanylyl cyclase‐C receptor mRNA distribution along the rat nephron. Regul Pept 95: 65‐74, 2000.
 21. Cha JH, Woo SK, Han KH, Kim YH, Handler JS, Kim J, Kwon HM. Hydration status affects nuclear distribution of transcription factor tonicity responsive enhancer binding protein in rat kidney. J Am Soc Nephrol 12: 2221‐2230, 2001.
 22. Chou CL, Knepper MA, Layton HE. Urinary concentrating mechanism ‐ the role of the inner medulla. Semin Nephrol 13: 168‐181, 1993.
 23. Chou CL, Knepper MA, Van Hoek AN, Brown D, Ma T, Verkman AS. Reduced water permeability and altered ultrastructure in thin descending limb of Henle in aquaporin‐1 null mice. J Clin Invest 103: 491‐496, 1999.
 24. Chou CL, Yip KP, Michea L, Kador K, Ferraris JD, Wade JB, Knepper MA. Regulation of aquaporin‐2 trafficking by vasopressin in the renal collecting duct ‐ roles of ryanodine‐sensitive Ca2+ stores and calmodulin. J Biol Chem 275: 36839‐36846, 2000.
 25. Chou C‐L, Knepper MA. In vitro perfusion of chinchilla thin limb segments: Segmentation and osmotic water permeability. Am J Physiol 263(3): F417‐F426, 1992.
 26. Chou C‐L, Knepper MA. In vitro perfusion of chinchilla thin limb segments: Urea and NaCl permeabilities. Am J Physiol 264: F337‐F343, 1993.
 27. Chou C‐L, Nielsen S, Knepper MA. Structural‐functional correlation in chinchilla long loop of Henle thin limbs: A novel papillary subsegment. Am J Physiol Renal 265: F863‐F874, 1993.
 28. Cowley AW, Jr. Role of the renal medulla in volume and arterial pressure regulation. Am J Physiol Regul Integr Comp Physiol 273: R1‐R15, 1997.
 29. Dantzler WH, Evans KK, Pannabecker TL. Osmotic water permeabilities in specific segments of rat inner medullary thin limbs of Henle's loops. FASEB J 23: 970.3, 2009.
 30. Dantzler WH, Kim YK, Abbott DE, Serrano OK, Brokl OH. Intracellular pH in isolated rat renal papillary thin limbs of Henle's loop. Pflugers Arch 440: 140‐148, 2000.
 31. Dantzler WH, Silbernagl S. Amino acid transport by juxtamedullary nephrons: Distal reabsorption and recycling. Am J Physiol 255: F397‐F407, 1988.
 32. Dantzler WH, Silbernagl S. Amino acid transport: Microinfusion and micropuncture of Henle's loops and vasa recta. Am J Physiol 258: F504‐F513, 1990.
 33. Estevez R, Bottger T, Stein V, Birkenhager R, Otto E, Hildebrandt F, Jentsch TJ. Barttin is a Cl‐ channel beta‐subunit crucial for renal Cl‐ reabsorption and inner ear K +secretion. Nature 414: 558‐561, 2001.
 34. Fenton RA, Brond L, Nielsen S, Praetorius J. Cellular and subcellular distribution of the type‐2 vasopressin receptor in the kidney. Am J Physiol Renal Physiol 293: F748‐F760, 2007.
 35. Fenton RA, Chou C‐L, Stewart GS, Smith CP, Knepper MA. Urinary concentrating defect in mice with selective deletion of phloretin‐sensitive urea transporters in the renal collecting duct. Proc Natl Acad Sci U S A 101: 7469‐7474, 2004.
 36. Fenton RA, Knepper MA. Mouse models and the urinary concentrating mechanism in the new millennium. Physiol Rev 87: 1083‐1112, 2007.
 37. Fenton RA, Stewart GS, Carpenter B, Howorth A, Potter EA, Cooper GJ, Smith CP. Characterization of mouse urea transporters UT‐A1 and UT‐A2. Am J Physiol Renal Physiol 283: F817‐F825, 2002.
 38. Fischer M, Janssen AGH, Fahlke C. Barttin activates CIC‐K channel function by modulating gating. J Am Soc Nephrol 21: 1281‐1289, 2010.
 39. Fujiwara I, Kondo Y, Igarashi Y, Inoue CN, Takahashi N, Tada K, Abe K. Amiloride‐sensitive Na+/H+ antiporter in basolateral membrane of hamster ascending thin limb of Henle's loop. Am J Physiol 268: F410‐F415, 1995.
 40. Furuse M, Tsukita S. Claudins in occluding junctions of humans and flies. Trends Cell Biol 16: 181‐188, 2006.
 41. Gonzalez‐Mariscal L, Namorado MC, Martin D, Luna J, Alarcon L, Islas S, Valencia L, Muriel P, Ponce L, Reyes JL. Tight junction proteins ZO‐1, ZO‐2, and occludin along isolated renal tubules. Kidney Int 57: 2386‐2402, 2000.
 42. Gottschalk CW, Mylle M. Micropuncture study of the mammalian urinary concentrating mechanism: Evidence for the countercurrent hypothesis. Am J Physiol 196: 927‐936, 1959.
 43. Han JS, Thompson KA, Chou C‐L, Knepper MA. Experimental tests of three‐dimensional model of urinary concentrating mechanism. J Am Soc Nephrol 2(12): 1677‐1688, 1992.
 44. Hanner F, Schnichels M, Zheng‐Fischhofer Q, Yang LE, Toma I, Willecke K, McDonough AA, Peti‐Peterdi J. Connexin 30.3 is expressed in the kidney but not regulated by dietary salt or high blood pressure. Cell Commun Adhes 15: 219‐230, 2008.
 45. Hoffert JD, Chou CL, Fenton RA, Knepper MA. Calmodulin is required for vasopressin‐stimulated increase in cyclic AMP production in inner medullary collecting duct. J Biol Chem 280: 13624‐13630, 2005.
 46. Humbert F, Pricam C, Perrelet A, Orci L. Freeze‐fracture differences between plasma‐membranes of descending and ascending branches of rat Henles thin loop. Lab Invest 33: 407‐411, 1975.
 47. Imai M. Function of the thin ascending limb of Henle of rats and hamsters perfused in vitro. Am J Physiol 232: F201‐F209, 1977.
 48. Imai M. Functional heterogeneity of the descending limbs of Henle's loop. ii. Interspecies differences among rabbits, rats, and hamsters. Pflugers Arch 402: 393‐401, 1984.
 49. Imai M, Hayashi M, Araki M. Functional heterogeneity of the descending limbs of Henle's loop. I. Internephron heterogeneity in the hamster kidney. Pflugers Arch 402: 385‐392, 1984.
 50. Imai M, Kokko JP. Sodium chloride, urea, and water transport in the thin ascending limb of Henle. Generation of osmotic gradients by passive diffusion of solutes. J Clin Invest 53: 393‐402, 1974.
 51. Imai M, Taniguchi J, Tabei K. Function of thin loops of Henle. Kidney Int 31: 565‐579, 1987.
 52. Imai M, Taniguchi J, Yoshitomi K. Transition of permeability properties along the descending limb of long‐loop nephron. Am J Physiol 254: F323‐F328, 1988.
 53. Imai M, Yasoshima K, Yoshitomi K. Mechanism of water transport across the upper portion of the descending thin limb of long‐looped nephron of hamsters. Pflugers Arch 415: 630‐637, 1990.
 54. Imai M, Yoshitomi K. Heterogeneity of the descending thin limb of Henle's loop. Kidney Int 38: 687‐694, 1990.
 55. Iwaki T, Kume‐Iwaki A, Goldman JE. Cellular distribution of αB‐crystallin in non‐lenticular tissues. J Histochem Cytochem 38: 31‐39, 1990.
 56. Jamison RL. Short and long loop nephrons. Kidney Int 31: 597‐605, 1987.
 57. Jamison RL, Kriz W. Urinary Concentrating Mechanism. New York: Oxford University Press, 1982.
 58. Jenq W, Mathieson IM, Ihara W, Ramirez G. Aquaporin‐1: An osmoinducible water channel in cultured mIMCD‐3 cells. Biochem Biophys Res Comm 245: 804‐809, 1998.
 59. Jentsch TJ, Stein V, Weinreich F, Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 82: 503‐568, 2002.
 60. Johnston PA, Battilana CA, Lacy FB, Jamison RL. Evidence for a concentration gradient favoring outward movement of sodium from the thin loop of Henle. J Clin Invest 59: 234‐240, 1977.
 61. Jung JY, Madsen KM, Han KH, Yang CW, Knepper MA, Sands JM, Kim J. Expression of urea transporters in potassium‐depleted mouse kidney. Am J Physiol Renal Physiol 285: F1210‐F1224, 2003.
 62. Kaissling B, Kriz W. Structural analysis of the rabbit kidney. Adv Anat Embryol Cell Biol 56: 1‐123, 1979.
 63. Kaissling B, Kriz W. Morphology of the loop of Henle, distal tubule, and collecting duct. In: Windhager EE, editor. Handbook of Physiology. New York: Oxford University Press, 1992, Sec. 8, pp. 109‐167.
 64. Kashgarian M, Biemesderfer D, Caplan M, Forbush B III. Monoclonal antibody to Na,K‐ATPase: Immunocytochemical localization along nephron segments. Kidney Int 28: 899‐913, 1985.
 65. Kersting U, Dantzler WH, Oberleithner H, Silbernagl S. Evidence for an acid pH in rat renal inner medulla: Paired measurements with liquid ion‐exchange microelectrodes on collecting ducts and vasa recta. Pflugers Arch 426: 354‐356, 1994.
 66. Kieferle S, Fong PY, Bens M, Vandewalle A, Jentsch TJ. Two highly homologous members of the ClC chloride channel family in both rat and human kidney. Proc Natl Acad Sci U S A 91: 6943‐6947, 1994.
 67. Kim J, Pannabecker TL. Two‐compartment model of inner medullary vasculature supports dual modes of vasopressin‐regulated inner medullary blood flow. Am J Physiol Renal Physiol, 299: F273‐F279, 2010.
 68. Kim YH, Kim DU, Han KH, Jung JY, Sands JM, Knepper MA, Madsen KM, Kim J. Expression of urea transporters in the developing rat kidney. Am J Physiol Renal Physiol 282: F530‐F540, 2002.
 69. Kiuchi‐Saishin Y, Gotoh S, Furuse M, Takasuga A, Tano Y, Tsukita S. Differential expression patterns of claudins, tight junction membrane proteins, in mouse nephron segments. J Am Soc Nephrol 13: 875‐886, 2002.
 70. Klein JD, Le Quach D, Cole JM, Disher K, Mongiu AK, Wang XD, Bernstein KE, Sands JM. Impaired urine concentration and absence of tissue ACE: Involvement of medullary transport proteins. Am J Physiol Renal Physiol 283: F517‐F524, 2002.
 71. Knepper MA, Danielson RA, Saidel GM, Post RS. Quantitative analysis of renal medullary anatomy in rats and rabbits. Kidney Int 12: 313‐323, 1977.
 72. Knepper MA, Roch‐Ramel F. Pathways of urea transport in the mammalian kidney. Kidney Int 31: 629‐633, 1987.
 73. Knepper MA, Saidel GM, Hascall VC, Dwyer T. Concentration of solutes in the renal inner medulla: Interstitial hyaluronan as a mechano‐osmotic transducer. Am J Physiol Renal Physiol 284: F433‐F446, 2003.
 74. Kokko JP. Sodium chloride and water transport in the descending limb of Henle. J Clin Invest 49: 1838‐1846, 1970.
 75. Kokko JP. Urea transport in the proximal tubule and the descending limb of Henle. J Clin Invest 51: 1999‐2008, 1972.
 76. Kokko JP, Rector FC. Countercurrent multiplication system without active transport in inner medulla. Kidney Int 2: 214‐223, 1972.
 77. Kondo Y, Yoshitomi K, Imai M. Effect of pH on Cl‐ transport in TAL of Henle's loop. Am J Physiol 253: F1216‐F1222, 1987.
 78. Kondo Y, Yoshitomi K, Imai M. Effect of Ca2+ on Cl‐ transport in thin ascending limb of Henle's loop. Am J Physiol 254: F232‐F239, 1988.
 79. Koyama S, Yoshitomi K, Imai M. Effect of protamine on ion conductance of ascending thin limb of Henle's loop from hamsters. Am J Physiol 261: F593‐F599, 1991a.
 80. Koyama S, Yoshitomi K, Imai M. Effect of protamine on ion conductance of upper portion of descending limb of long‐looped nephron from hamsters. Am J Physiol 260: F839‐F847, 1991b.
 81. Kriz W. Structural organization of the renal medulla: Comparative and functional aspects. Am J Physiol 241: R3‐R16, 1981.
 82. Kriz W, Bankir L. A standard nomenclature for structures of the kidney. Am J Physiol 254: F1‐F8, 1988.
 83. Kriz W, Kaissling B. Structural organization of the mammalian kidney. In: Seldin DW, Giebisch G, editors. The Kidney: Physiology and Pathophysiology. New York: Raven Press Ltd., 1992, pp. 707‐777.
 84. Kriz W, Schnermann J, Koepsell H. The position of short and long loops of Henle in the rat kidney. Z Anat Entwickl‐Gesch 138: 301‐319, 1972.
 85. Kurtz I. Apical and basolateral Na+/H+ exchange in the rabbit outer medullary thin descending limb of Henle: Role of intracellular pH regulation. J Membr Biol 106: 253‐260, 1988.
 86. Kwon O, Myers BD, Sibley R, Dafoe D, Alfrey E, Nelson WJ. Distribution of cell membrane‐associated proteins along the human nephron. J Histochem Cytochem 46: 1423‐1434, 1998.
 87. Lam AKM, Ko BCB, Tam S, Morris R, Yang JY, Chung SK, Chung SSM. Osmotic response element‐binding protein (OREBP) is an essential regulator of the urine concentrating mechanism. J Biol Chem 279: 48048‐48054, 2004.
 88. Lassiter WE, Gottschalk CW, Mylle M. Micropuncture study of net transtubular movement of water and urea in nondiuretic mammalian kidney. Am J Physiol 200: 1139‐1147, 1961.
 89. Layton AT, Layton HE. A region‐based mathematical model of the urine concentrating mechanism in the rat outer medulla. I. Formulation and base‐case results. Am J Physiol 289: F1346‐F1366, 2005.
 90. Layton AT, Layton HE, Dantzler WH, Pannabecker TL. The mammalian urine concentrating mechanism: Hypotheses and uncertainties. Physiology 24: 250‐256, 2009.
 91. Layton AT, Pannabecker TL, Dantzler WH, Layton HE. Two modes for concentrating urine in rat inner medulla. Am J Physiol Renal Physiol 287: F816‐F839, 2004.
 92. Layton AT, Pannabecker TL, Dantzler WH, Layton HE. Functional implications of the three‐dimensional architecture of the rat renal inner medulla. Am J Physiol Renal Physiol 298: F973‐F987, 2010.
 93. Layton HE. Distribution of Henle's loops may enhance urine concentrating capability. Biophys J 49: 1033‐1040, 1986.
 94. Layton HE. Concentrating urine in the inner medulla of the kidney. Comments Theor Biol 1: 179‐196, 1989.
 95. Layton HE, Davies JM. Distributed solute and water reabsorption in a central core model of the renal medulla. Math Biosci 116: 169‐196, 1993.
 96. Layton HE, Knepper MA, Chou CL. Permeability criteria for effective function of passive countercurrent multiplier. Am J Physiol 270: F9‐F20, 1996.
 97. Lemley KV, Kriz W. Cycles and separations: The histotopography of the urinary concentrating process. Kidney Int 31: 538‐548, 1987.
 98. Leroy C, Basset G, Gruel G, Ripoche P, Trinh‐Trang‐Tan MM, Rousselet G. Hyperosmotic NaCl and urea synergistically regulate the expression of the UT‐A2 urea transporter in vitro and in vivo. Biochem Biophys Res Comm 271: 368‐373, 2000.
 99. Li WY, Huey CL, Yu AS. Expression of claudin‐7 and ‐8 along the mouse nephron. Am J Physiol Renal Physiol 286: F1063‐F1071, 2004.
 100. Liantonio A, Picollo A, Carbonara G, Fracchiolla G, Tortorella P, Loiodice F, Laghezza A, Babini E, Zifarelli G, Pusch M, Camerino DC. Molecular switch for CLC‐K Cl‐ channel block/activation: Optimal pharmacophoric requirements towards high‐affinity ligands. Proc Natl Acad Sci U S A 105: 1369‐1373, 2008.
 101. Lim S‐W, Han K‐H, Jung J‐Y, Kim W‐Y, Yang C‐W, Sands JM, Knepper MA, Madsen KM, Kim J. Ultrastructural localization of UT‐A, UT‐B in rat kidneys with different hydration status. Am J Physiol Regul Integr Comp Physiol 290: R479‐R492, 2006.
 102. Liu W, Morimoto T, Kondo Y, Iinuma K, Uchida S, Imai M. “Avian‐type” renal medullary tubule organization causes immaturity of urine‐concentrating ability in neonates. Kidney Int 60: 680‐693, 2001.
 103. Liu W, Morimoto T, Kondo Y, Iinuma K, Uchida S, Sasaki S, Marumo F, Imai M. Analysis of NaCl transport in thin ascending limb of Henle's loop in CLC‐K1 null mice. Am J Physiol Renal Physiol 282: F451‐F457, 2002.
 104. Lopes AG, Amzel LM, Markakis D, Guggino WB. Cell‐volume regulation by the thin descending‐limb of Henles loop. Proc Natl Acad Sci U S A 85: 2873‐2877, 1988.
 105. Maeda Y, Smith BL, Agre P, Knepper MA. Quantification of aquaporin‐CHIP water channel protein in microdissected renal tubules by fluorescence‐based ELISA. J Clin Invest 95: 422‐428, 1995.
 106. Marin‐Castano ME, Schanstra JP, Neau E, Praddaude F, Pecher C, Ader JL, Girolami JP, Bascands JL. Induction of functional bradykinin B‐1‐receptors in normotensive rats and mice under chronic angiotensin‐ converting enzyme inhibitor treatment. Circ 105: 627‐632, 2002.
 107. Marsh DJ. Solute and water flows in thin limbs of Henle's loop in the hamster kidney. Am J Physiol 218: 824‐831, 1970.
 108. Marsh DJ, Azen SP. Mechanism of NaCl reabsorption by hamster thin ascending limbs of Henle's loop. Am J Physiol 228: 71‐79, 1975.
 109. Marsh DJ, Solomon S. Analysis of electrolyte movement in thin Henle's loops of hamster papilla. Am J Physiol 208: 1119‐1128, 1965.
 110. Matsumura Y, Uchida S, Kondo Y, Miyazaki H, Ko SBH, Hayama A, Morimoto T, Liu W, Arisawa M, Sasaki S, Marumo F. Overt nephrogenic diabetes insipidus in mice lacking the CLC‐K1 chloride channel. Nat Genet 21: 95‐98, 1999.
 111. Mejia R, Wade JB. Immunomorphometric study of rat renal inner medulla. Am J Physiol Renal Physiol 282: F553‐F557, 2002.
 112. Michl M, Ouyang N, Fraek ML, Beck FX, Neuhofer W. Expression and regulation of alpha B‐crystallin in the kidney in vivo and in vitro. Pflugers Archiv 452: 387‐395, 2006.
 113. Moffat DB, Fourman J. The vascular pattern of the rat kidney. J Anat 97: 543‐553, 1963.
 114. Morel F, Imbert‐Teboul M, Chabardes D. Receptors to vasopressin and other hormones in the mammalian kidney. Kidney Int 31: 512‐520, 1987.
 115. Morgan T. A microperfusion study in the rat of the permeability of the papillary segments of the nephron to Na24. Clin Exp Pharmacol Physiol 1: 23‐30, 1974.
 116. Morgan T, Berliner RW. Permeability of the loop of Henle, vasa recta, and collecting duct to water, urea, and sodium. Am J Physiol 215: 108‐115, 1968.
 117. Moridaira K, Nodera M, Sato G, Yanagisawa H. Detection of Prepro‐ET‐1 mRNA in normal rat kidney by in situ RT‐PCR. Nephron Exp Nephrol 95: E55‐E61, 2003.
 118. Nielsen S, Frokiaer J, Marples D, Kwon TH, Agre P, Knepper MA. Aquaporins in the kidney: From molecules to medicine. Physiol Rev 82: 205‐244, 2002.
 119. Nielsen S, Smith BL, Christensen EI, Knepper MA, Agre P. Chip28 water channels are localized in constitutively water‐permeable segments of the nephron. J Cell Biol 120: 371‐383, 1993.
 120. Nielsen S, Terris J, Smith CP, Hediger MA, Ecelbarger CA, Knepper MA. Cellular and subcellular localization of the vasopressin‐ regulated urea transporter in rat kidney. Proc Natl Acad Sci U S A 93: 5495‐5500, 1996.
 121. Nishimura H. Urine concentration and avian aquaporin water channels. Pflugers Archiv 456: 755‐768, 2008.
 122. Ong ACM, Jowett TP, Firth JD, Burton S, Karet FE, Fine LG. An endothelin‐1 mediated autocrine growth loop involved in human renal tubular regeneration. Kidney Int 48: 390‐401, 1995.
 123. Pallone TL, Turner MR, Edwards A, Jamison RL. Countercurrent exchange in the renal medulla. Am J Physiol Regul Integr Comp Physiol 284: R1153‐R1175, 2003.
 124. Pannabecker TL. Loop of Henle interaction with interstitial nodal spaces in the renal inner medulla. Am J Physiol Renal Physiol 295: F1744‐F1751, 2008.
 125. Pannabecker TL, Abbott DE, Dantzler WH. Three‐dimensional functional reconstruction of inner medullary thin limbs of Henle's loop. Am J Physiol Renal Physiol 286: F38‐F45, 2004.
 126. Pannabecker TL, Brokl OH, Kim YK, Abbott DE, Dantzler WH. Regulation of intracellular pH in rat renal inner medullary thin limbs of Henle's loop. Pflugers Arch 443: 446‐457, 2002.
 127. Pannabecker TL, Dahlmann A, Brokl OH, Dantzler WH. Mixed descending‐ and ascending‐type thin limbs of Henle's loop in mammalian renal inner medulla. Am J Physiol Renal Physiol 278: F202‐F208, 2000.
 128. Pannabecker TL, Dantzler WH. Three‐dimensional lateral and vertical relationships of inner medullary loops of Henle and collecting ducts. Am J Physiol Renal Physiol 287: F767‐F774, 2004.
 129. Pannabecker TL, Dantzler WH. Three‐dimensional architecture of inner medullary vasa recta. Am J Physiol Renal Physiol 290: F1355‐F1366, 2006.
 130. Pannabecker TL, Dantzler WH. Three‐dimensional architecture of collecting ducts, loops of Henle, and blood vessels in the renal papilla. Am J Physiol Renal Physiol 293: F696‐F704, 2007.
 131. Pannabecker TL, Dantzler WH, Layton HE, Layton AT. Role of three‐dimensional architecture in the urine concentrating mechanism of the rat renal inner medulla. Am J Physiol Renal Physiol 295: F1271‐F1285, 2008.
 132. Pannabecker TL, Henderson C, Dantzler WH. Quantitative analysis of functional reconstructions reveals lateral and axial zonation in the renal inner medulla. Am J Physiol Renal Physiol 294: 1306‐1314, 2008.
 133. Pannabecker TL, Völker K, Silbernagl S, Dantzler WH. Cycloleucine fluxes during rat vasa recta and loop microinfusions in vivo and loop microperfusions in vitro. Pflugers Arch 439: 517‐523, 2000.
 134. Pennell JP, Lacy FB, Jamison RL. An in vivo study of the concentrating process in the descending limb of Henle's loop. Kidney Int 5: 337‐347, 1974.
 135. Pennell JP, Sanjana V, Frey NR, Jamison RL. The effect of urea infusion on the urinary concentrating mechanism in protein‐depleted rats. J Clin Invest 55: 399‐409, 1975.
 136. Piepenhagen PA, Peters LL, Lux SE, Nelson WJ. Differential expression of Na+‐K+‐ATPase, ankyrin, fodrin, and E‐cadherin along the kidney nephron. Am J Physiol Cell Physiol 269: C1417‐C1432, 1995.
 137. Pihakaski‐Maunsbach K, Vorum H, Honore B, Tokonabe S, Frokiaer J, Garty H, Karlish SJD, Maunsbach AB. Locations, abundances, and possible functions of FXYD ion transport regulators in rat renal medulla. Am J Physiol Renal Physiol 291: F1033‐F1044, 2006.
 138. Preston GM, Carroll TP, Guggino WB, Agre P. Appearance of water channels in Xenopus oocytes expressing red‐cell Chip28 protein. Sci 256: 385‐387, 1992.
 139. Promeneur D, Bankir L, Hu MC, Trinh‐Trang‐Tan M‐M. Renal tubular and vascular urea transporters: Influence of antidiuretic hormone on messenger RNA expression in Brattleboro rats. J Am Soc Nephrol 9: 1359‐1366, 1998.
 140. Pupilli C., Brunori M, Misciglia N, Selli C, Ianni L, Yanagisawa M, Mannelli M, Serio M. Presence and distribution of endothelin‐1 gene expression in human kidney. Am J Physiol Renal Physiol 267: F679‐F687, 1994.
 141. Reinking LN, Schmidt‐Nielsen B. Peristaltic flow of urine in the renal papillary collecting ducts of hamsters. Kidney Int 20: 55‐60, 1981.
 142. Rollhauser H, Kriz W, Heinke W. Das gefass‐system der rattenniere. Z Zellforsch 64: 381‐403, 1964.
 143. Sabolic I, Herak‐Kramberger CM, Breton S, Brown D. Na/K‐ATPase in intercalated cells along the rat nephron revealed by antigen retrieval. J Am Soc Nephrol 10: 913‐922, 1999.
 144. Sands JM, Kokko JP, Jacobson HR. Intrarenal heterogeneity: Vascular and tubular. In: Seldin DW, Giebisch G, editors. The Kidney: Physiology and Pathophysiology. New York: Raven, 1992, pp. 1087‐1155.
 145. Sands JM, Layton HE. The urine concentrating mechanism and urea transporters. In: Alpern RJ, Hebert SC, editors. The Kidney: Physiology and Pathophysiology. Philadelphia: Elsevier, 2007, pp. 1143‐1177.
 146. Sands JM, Nonoguchi H, Knepper MA. Vasopressin effects on urea and H2O transport in inner medullary collecting duct subsegments. Am J Physiol 253: F823‐F832, 1987.
 147. Sands JM, Nonoguchi H, Knepper MA. Hormone effects on NaCl permeability of rat inner medullary collecting duct. Am J Physiol 255(3): F421‐F428, 1988.
 148. Sands JM, Terada Y, Bernard LM, Knepper MA. Aldose reductase activities in microdissected rat renal tubule segments. Am J Physiol 256(4): F563‐F569, 1989.
 149. Schmidt‐Nielsen B, Graves B. Changes in fluid compartments in hamster renal papilla due to peristalsis in the pelvic wall. Kidney Int 22: 613‐625, 1982.
 150. Schneeberger EE, Lynch RD. The tight junction: A multifunctional complex. Am J Physiol Cell Physiol 286: C1213‐C1228, 2004.
 151. Scholl U, Hebeisen S, Janssen AGH, Mueller‐Newen G, Alekov A, Fahlke C. Barttin modulates trafficking and function of ClC‐K channels. Proc Natl Acad Sci U S A 103: 11411‐11416, 2006.
 152. Schwartz MM, Karnovsky MJ, Venkatachalam MA. Regional membrane specialization in the thin limbs of Henle loops as seen by freeze‐fracture electron‐microscopy. Kidney Int 16: 577‐589, 1979.
 153. Schwartz MM, Venkatachalam MA. Structural differences in thin limbs of Henle: Physiological implications. Kidney Int 6: 193‐208, 1974.
 154. Shayakul C, Knepper MA, Smith CP, DiGiovanni SR, Hediger MA. Segmental localization of urea transporter mRNAs in rat kidney. Am J Physiol Renal Physiol 272: F654‐F660, 1997.
 155. Smith CP, Lee WS, Martial S, Knepper MA, You GF, Sands JM, Hediger MA. Cloning and regulation of expression of the rat‐kidney urea transporter (Rut2). J Clin Invest 96: 1556‐1563, 1995.
 156. Stephenson JL. Concentration of urine in a central core model of the renal counterflow system. Kidney Int 2: 85‐94, 1972.
 157. Takada T, Yamamoto A, Omori K, Tashiro Y. Quantitative immunogold localization of Na, K‐ATPase along rat nephron. Histochem 98: 183‐197, 1992.
 158. Takahashi N, Kondo Y, Fujiwara I, Ito O, Igarashi Y, Abe K. Characterization of Na+ transport across the cell membranes of the ascending thin limb of Henle's loop. Kidney Int 47: 789‐794, 1995.
 159. Takahashi N, Kondo Y, Ito O, Igarashi Y, Omata K, Abe K. Vasopressin stimulates Cl− transport in ascending thin limb of Henle's loop in hamster. J Clin Invest 95: 1623‐1627, 1995.
 160. Terada Y, Tomita K, Nonoguchi H, Marumo F. Polymerase chain reaction localization of constitutive nitric oxide synthase and soluble guanylate cyclase messenger RNAs in microdissected rat nephron segments. J Clin Invest 90: 659‐665, 1992.
 161. Terada Y, Tomita K, Nonoguchi H, Yang TX, Marumo F. Expression of endothelin‐3 messenger‐RNA along rat nephron segments using polymerase chain‐reaction. Kidney Int 44: 1273‐1280, 1993.
 162. Thomson RB, Igarashi P, Biemesderfer D, Kim R, Abualfa A, Soleimani M, Aronson PS. Isolation and cDNA cloning of Ksp‐cadherin, a novel kidney‐specific member of the cadherin multigene family. J Biol Chem 270: 17594‐17601, 1995.
 163. Thorens B. Facilitated glucose transporters in epithelial‐cells. Annu Rev Physiol 55: 591‐608, 1993.
 164. Thorens B, Lodish HF, Brown D. Differential localization of two glucose transporter isoforms in rat kidney. Am J Physiol Cell Physiol 259: C286‐C294, 1990.
 165. Tom B, Dendorfer A, Danser AHJ. Bradykinin, angiotensin‐(1‐7), and ACE inhibitors: how do they interact? Int J Biochem Cell Biol 35: 792‐801, 2003.
 166. Tsukita S, Furuse M, Itoh M. Multifunctional strands in tight junctions. Nat Rev Mol Cell Biol 2: 285‐293, 2001.
 167. Uchida S, Endou H. Substrate specificity to maintain cellular ATP along the mouse nephron. Am J Physiol 255: F977‐F983, 1988.
 168. Uchida S, Sasaki S, Furakawa T, Hiraoka M, Imai T, Hirata Y, Marumo F. Molecular cloning of a chloride channel that is regulated by dehydration and expressed predominantly in the kidney medulla. J Biol Chem 268: 3821‐3824, 1993.
 169. Uchida S, Sasaki S, Nitta K, Uchida K, Horita S, Nihei H, Marumo F. Localization and functional characterization of rat kidney‐specific chloride channel. J Clin Invest 95: 104‐113, 1995.
 170. Uchida S, Sohara E, Rai T, Ikawa M, Okabe M, Sasaki M. Impaired urea accumulation in the inner medulla of mice lacking the urea transporter UT‐A2. Mol Cell Biol 25: 7357‐7363, 2005.
 171. Umenishi F, Schrier RW. Hypertonicity‐induced aquaporin‐1 (AQP1) expression is mediated by the activation of MAPK pathways and hypertonicity‐responsive element in the AQP1 gene. J Biol Chem 278: 15765‐15770, 2010.
 172. Van Itallie CM, Fanning AS, Bridges A, Anderson JM. ZO‐1 stabilizes the tight junction solute barrier through coupling to the perijunctional cytoskeleton. Mol Biol Cell 20: 3930‐3940, 2009.
 173. Van Itallie CM, Rogan S, Yu A, Vidal LS, Holmes J, Anderson JM. Two splice variants of claudin‐10 in the kidney create paracellular pores with different ion selectivities. Am J Physiol Renal Physiol 291: F1288‐F1299, 2006.
 174. Vandewalle A, Cluzeaud F, Bens M, Kieferle S, Steinmeyer K, Jentsch TJ. Localization and induction by dehydration of ClC‐K chloride channels in the rat kidney. Am J Physiol 272: F678‐F688, 1997.
 175. Verbavatz JM, Brown D, Sabolic I, Valenti G, Ausiello DA, Vanhoek AN, Ma T, Verkman AS. Tetrameric assembly of Chip28 water channels in liposomes and cell‐membranes ‐ a freeze‐fracture study. J Cell Biol 123: 605‐618, 1993.
 176. Wade JB, Lee AJ, Liu C, Ecelbarger C, Mitchell C, Bradford AD, Terris J, Kim G‐H, Knepper MA. UT‐A2: A 55‐kDa urea transporter in thin descending limb whose abundance is regulated by vasopressin. Am J Physiol 278: F52‐F62, 2000.
 177. Waldegger S, Busch AE, Kern C, Capasso G, Murer H, Lang F. Function and dysfunction of renal transport molecules: Lessons from electrophysiology. Renal Physiol Biochem 19: 155‐159, 1996.
 178. Wetzel RK, Sweadner KJ. Immunocytochemical localization of Na‐K‐ATPase alpha‐ and gamma‐subunits in rat kidney. Am J Physiol Renal Physiol 281: F531‐F545, 2001.
 179. Wilkes BM, Susin M, Mento PF, Macica CM, Girardi EP, Boss E, Nord EP. Localization of endothelin‐like immunoreactivity in rat kidneys. Am J Physiol 260: F913‐F920, 1991.
 180. Wolf K, Meier‐Meitinger M, Bergler T, Castrop H, Vitzthum H, Riegger GAJ, Kurtz A, Kramer BK. Parallel down‐regulation of chloride channel ClC‐K1 and barttin mRNA in the thin ascending limb of the rat nephron by furosemide. Pflugers Arch 446: 665‐671, 2003.
 181. Wu F, Park F, Cowley AW, Mattson DL. Quantification of nitric oxide synthase activity in microdissected segments of the rat kidney. Am J Physiol Renal Physiol 276: F874‐F881, 1999.
 182. Yool AJ, Brokl OH, Pannabecker TL, Dantzler WH, Stamer WD. Tetraethylammonium block of water flux in aquaporin‐1 channels expressed in kidney thin limbs of Henle's loop and a kidney‐derived cell line. BMC Physiol 2: 4, 2002.
 183. You G, Smith CP, Kanai Y, Lee W‐S, Stelzner M, Hediger MA. Cloning and characterization of the vasopressin‐regulated urea transporter. Nature 365: 844‐847, 1993.
 184. Zhai X‐Y, Thomsen JS, Birn H, Kristoffersen IB, Andreasen A, Christensen EI. Three‐dimensional reconstruction of the mouse nephron. J Am Soc Nephrol 17: 77‐88, 2006.
 185. Zhai XY, Fenton RA, Andreasen A, Thomsen JS, Christensen EI. Aquaporin‐1 is not expressed in descending thin limbs of short‐loop nephrons. J Am Soc Nephrol 18: 2937‐2944, 2007.

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Thomas L. Pannabecker. Structure and Function of the Thin Limbs of the Loop of Henle. Compr Physiol 2012, 2: 2063-2086. doi: 10.1002/cphy.c110019