An examination of transcapillary water flux in renal inner medulla

Sanjana, VM; Pa, Johnston; Robertson, C R; Jamison, Rex L.

doi:10.1152/ajplegacy.1976.231.2.313

Cited by 36 publications

(27 citation statements)

References 4 publications

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“…The rats remained nondiuretic throughout the study as indicated by the mean ratios for urine-to-systemic plasma osmolality and urine-to-systemic plasma inulin. (21) and, in a later study (22), of VR at the papillary tip were slightly lower than 7 g/100 ml. In correcting the present data for plasma water we used the highest mean value.…”

Section: Resultsmentioning

confidence: 62%

“…If the protein concentration in medullary interstitial fluid is less than that in VR plasma (and there are reasonable grounds for assuming it is [22]), then the cation concentration in the interstitium is less than that in VR plasma water and the difference in sodium concentration between fluid in Henle's thin limb and the interstitium is greater than that calculated by neglecting the GibbsDonnan equilibrium. Therefore use of VR plasma sodium concentration uncorrected for the GibbsDonnan distribution will underestimate the actual loop fluid-vasa recta plasma (LH-VR) sodium gradient.…”

Section: Resultsmentioning

confidence: 99%

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Evidence for a concentration gradient favoring outward movement of sodium from the thin loop of Henle.

Johnston¹,

Battilana²,

Lacy³

et al. 1977

J. Clin. Invest.

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A B S T R A C T Recent models of the urinary concentrating mechanism have postulated that urea in the medullary interstitium creates a transtubular concentration gradient for sodium between fluid at the end of the descending limb of Henle's loop and the medullary interstitium, favoring the passive outward movement of sodium from Henle's thin ascending limb. These experiments were designed to determine whether such a gradient normally exists. Young nondiuretic Munich-Wistar rats were prepared for micropuncture of the exposed left renal papilla. Samples of loop of Henle fluid and vasa recta plasma (assumed to reflect the composition of interstitial fluid) were obtained from adjacent sites. Loop fluid values in 21 comparisons from 18 rats (mean+SE)were: sodium, 344+ 12 meq/liter; potassium, 26+2 meq/liter; osmolality, 938+37 mosmol/kg H20. Vasa recta plasma values (in corresponding units ofmeasurement) were: sodium, 284±11; potassium, 34±2; osmolality, 935±34. Mean values of paired differences (loop fluid minus vasa recta plasma) were: A sodium, 60±11.1 (P < 0.001); A potassium, -8.0±2.1 (P < 0.001); A osmolality, 4±16 (NS). Corrected for plasma water, the loop fluid minus vasa recta differences (in milliequivalents per kilogram H20) were:A sodium, 40±11.4 (P < 0.005); A potassium, -9.7 ±1.9 (P < 0.001). We interpret these findings to indicate that in the papilla of nondiuretic rats, a significant difference in sodium concentration exists across the thin loop of Henle favoring outward movement of sodium, which confirms a key requirement of the pasPortions of this work were presented to the American Society for Clinical Investigation.

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Section: Resultsmentioning

confidence: 62%

Section: Resultsmentioning

confidence: 99%

Evidence for a concentration gradient favoring outward movement of sodium from the thin loop of Henle.

Johnston¹,

Battilana²,

Lacy³

et al. 1977

J. Clin. Invest.

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“…These cells express the AQP1 water channel that is responsible for small-solute-driven efflux of water to the medullary interstitium (118,137). Thus, in opposition to the classic view of purely diffusive countercurrent exchange, water abstraction is an important mode of DVR equilibration.…”

Section: Discussionmentioning

confidence: 99%

“…That transport proceeds in a direction opposite to inwardly directed Starling forces (hydraulic and oncotic pressure), thus implicating transmural small-solute osmotic gradients as the responsible driving force (98,118,137,138). For NaCl and urea gradients generated by the lag in equilibration between DVR plasma and medullary interstitium to induce water efflux, the water must traverse a pathway of sufficiently small pore size for these solutes to be osmotically active.…”

Section: Transport Of Solutes and Water Across Vasa Rectamentioning

confidence: 99%

Physiology of the renal medullary microcirculation

Pallone

Zhang

Rhinehart

2003

American Journal of Physiology-Renal Physiology

187

193

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Pallone, Thomas L., Zhong Zhang, and Kristie Rhinehart. Physiology of the renal medullary microcirculation. Am J Physiol Renal Physiol 284: F253-F266, 2003; 10.1152/ajprenal.00304.2002.-Perfusion of the renal medulla plays an important role in salt and water balance. Pericytes are smooth muscle-like cells that impart contractile function to descending vasa recta (DVR), the arteriolar segments that supply the medulla with blood flow. DVR contraction by ANG II is mediated by depolarization resulting from an increase in plasma membrane Cl Ϫ conductance that secondarily gates voltage-activated Ca 2ϩ entry. In this respect, DVR may differ from other parts of the efferent microcirculation of the kidney. Elevation of extracellular K ϩ constricts DVR to a lesser degree than ANG II or endothelin-1, implying that other events, in addition to membrane depolarization, are needed to maximize vasoconstriction. DVR endothelial cytoplasmic Ca 2ϩ is increased by bradykinin, a response that is inhibited by ANG II. ANG II inhibition of endothelial Ca 2ϩ signaling might serve to regulate the site of origin of vasodilatory paracrine agents generated in the vicinity of outer medullary vascular bundles. In the hydropenic kidney, DVR plasma equilibrates with the interstitium both by diffusion and through water efflux across aquaporin-1. That process is predicted to optimize urinary concentration by lowering blood flow to the inner medulla. To optimize urea trapping, DVR endothelia express the UT-B facilitated urea transporter. These and other features show that vasa recta have physiological mechanisms specific to their role in the renal medulla. vasa recta; perfusion; hypertension; oxygenation; urinary concentration; patch clamp; calcium; fura 2 THE MICROCIRCULATION OF THE kidney is regionally specialized. In the cortex, afferent and efferent arterioles govern the driving forces that promote glomerular filtration. A dense peritubular capillary plexus arising from efferent arterioles surrounds the proximal and distal convoluted tubules to accommodate enormous reabsorption of glomerular filtrate. In contrast, vasa recta serve needs specific to the medulla. Through the counterflow arrangement of descending (DVR) and ascending vasa recta (AVR), countercurrent exchange traps NaCl and urea deposited to the interstitium by collecting ducts and the loops of Henle. This is vital to maintain corticomedullary osmotic gradients but conflicts with the need to supply nutrient blood flow to medullary tissue. Metabolic substrates that enter the medulla in DVR blood diffuse to the AVR to be shunted back to the cortex. To deal with the threat of medullary hypoxia resulting from this process, the kidney has evolved a capacity to exert subtle control over regional perfusion of the outer and inner medulla. The details are far from clear, but much experimental evidence points to the complex interactions of many autocoids and paracrine agents to modulate vasomotor tone at various sites along the microvascular circuit. The goal of this review is to summarize ...

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“…With respect to the transport of water, classical Starling forces (hydraulic and oncotic pressure) can drive water flux across outer medullary descending vasa recta (OMDVR) via a shared pathway where small hydrophilic solutes are also transported (6). In vivo, however, it has been shown that water efflux occurs across the descending vasa recta (DVR) wall at some location between the corticomedullary junction and papillary tip, despite the existence of Starling forces that favor volume influx (7). It was proposed that water efflux involves a water-only pathway in which NaCl and urea gradients are able to drive water movement, and that the water-only pathway might comprise aquaporin-1 (AQP1) water channels (8,9).…”

Section: Introductionmentioning

confidence: 99%

Requirement of aquaporin-1 for NaCl-driven water transport across descending vasa recta

Pallone¹,

Edwards²,

Ma³

et al. 2000

J. Clin. Invest.

116

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Deletion of AQP1 in mice results in diminished urinary concentrating ability, possibly related to reduced NaCl-and urea gradient-driven water transport across the outer medullary descending vasa recta (OMDVR). To quantify the role of AQP1 in OMDVR water transport, we measured osmotically driven water permeability in vitro in microperfused OMDVR from wild-type, AQP1 heterozygous, and AQP1 knockout mice. OMDVR diameters in AQP1 -/-mice were 1.9-fold greater than in AQP1 +/+ mice. Osmotic water permeability (P f ) in response to a 200 mM NaCl gradient (bath > lumen) was reduced about 2-fold in AQP1 +/-mice and by more than 50-fold in AQP1 -/-mice. P f increased from 1015 to 2527 µm/s in AQP1 +/+ mice and from 22 to 1104 µm/s in AQP1 -/-mice when a raffinose rather than an NaCl gradient was used. This information, together with p-chloromercuribenzenesulfonate inhibition measurements, suggests that nearly all NaCl-driven water transport occurs by a transcellular route through AQP1, whereas raffinose-driven water transport also involves a parallel, AQP1-independent, mercurial-insensitive pathway. Interestingly, urea was also able to drive water movement across the AQP1-independent pathway. Diffusional permeabilities to small hydrophilic solutes were comparable in AQP1 +/+ and AQP1 -/-mice but higher than those previously measured in rats. In a mathematical model of the medullary microcirculation, deletion of AQP1 resulted in diminished concentrating ability due to enhancement of medullary blood flow, partially accounting for the observed urine-concentrating defect.

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An examination of transcapillary water flux in renal inner medulla

Cited by 36 publications

References 4 publications

Evidence for a concentration gradient favoring outward movement of sodium from the thin loop of Henle.

Evidence for a concentration gradient favoring outward movement of sodium from the thin loop of Henle.

Physiology of the renal medullary microcirculation

Requirement of aquaporin-1 for NaCl-driven water transport across descending vasa recta

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