Hydraulic and diffusional permeabilities of isolated outer medullary descending vasa recta from the rat

Turner, M. R.; Pallone, Thomas L.

doi:10.1152/ajpheart.1997.272.1.h392

Cited by 21 publications

(29 citation statements)

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“…In the control group, fluorescence declines due to leakage of DAF-2 from the cytoplasm. Fluorescence is greater on exposure to BK (100 nM) and increases further when the bath contains the superoxide dismutase mimetic tempol (1 mM diffusive transport of NaCl and other small hydrophilic solutes (82,109,158). In addition to this, transcellular pathways have been identified that conduct transport of urea and water (51, 52, 92, 93, 97-99, 106, 108, 117, 118).…”

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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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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“…As will be discussed in subsequent sections, transport of water across the DVR wall is more rigorously described by simulating parallel pathways. One pathway is the highly selective AQP1 molecule ( ss ϭ 1.0) and a parallel pathway that conducts both water movement as well as convective and diffusive flux of small solutes ( ss Ϸ 0) (77,87,89,95,135). Expression of AQP1 in DVR has been hypothesized to play an important role in the optimization of renal medullary countercurrent exchanger function (87).…”

Section: Countercurrent Exchange-general Concepts and Evolution Of Unmentioning

confidence: 99%

“…Water moves through the walls of DVR via pathways of at least two kinds (77,89,90,135). Analysis of the permeabilities of DVR indicates that a "shared" transmural pathway for water and hydrophilic solutes exists in parallel with a "water only" pathway ( Ϸ 1.0) that excludes hydrophilic solutes.…”

Section: Transport Of Water Through the Dvr Wallmentioning

confidence: 99%

Countercurrent exchange in the renal medulla

Pallone

Turner

Edwards

et al. 2003

American Journal of Physiology-Regulatory, Integrative and Comp

139

102

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Pallone, Thomas L., Malcolm R. Turner, Auré lie Edwards, and Rex L. Jamison. Countercurrent exchange in the renal medulla. Am J Physiol Regul Integr Comp Physiol 284: R1153-R1175, 2003 10.1152/ ajpregu.00657.2002The microcirculation of the renal medulla traps NaCl and urea deposited to the interstitium by the loops of Henle and collecting ducts. Theories have predicted that countercurrent exchanger efficiency is favored by high permeability to solute. In contrast to the conceptualization of vasa recta as simple "U-tube" diffusive exchangers, many findings have revealed surprising complexity. Tubular-vascular relationships in the outer and inner medulla differ markedly. The wall structure and transport properties of descending vasa recta (DVR) and ascending vasa recta (AVR) are very different. The recent discoveries of aquaporin-1 (AQP1) water channels and the facilitated urea carrier UTB in DVR endothelia show that transcellular as well as paracellular pathways are involved in equilibration of DVR plasma with the interstitium. Efflux of water across AQP1 excludes NaCl and urea, leading to the conclusion that both water abstraction and diffusion contribute to transmural equilibration. Recent theory predicts that loss of water from DVR to the interstitium favors optimization of urinary concentration by shunting water to AVR, secondarily lowering blood flow to the inner medulla. Finally, DVR are vasoactive, arteriolar microvessels that are anatomically positioned to regulate total and regional blood flow to the outer and inner medulla. In this review, we provide historical perspective, describe the current state of knowledge, and suggest areas that are in need of further exploration. vasa recta; microperfusion; microcirculation; water channel; urinary concentration; permeability SINCE THE EXPERIMENTAL FINDINGS of Wirz et al. (147) led to the countercurrent theory of the urinary concentrating mechanism, as described by Hargitay and Kuhn (31), most subsequent research has focused on the countercurrent multiplier function of the loops of Henle. According to the theory, a small difference in osmotic pressure (the single effect) is multiplied by countercurrent flow in adjacent channels of the limbs of Henle's loop to produce a large axial difference in osmotic pressure between the renal cortex and the tip of the renal papilla; that is, the multiplier generates a hypertonic renal medulla. Less attention has been paid to countercurrent exchange, which is thought to preserve medullary hypertonicity rather than create it. It is generally accepted that the microcirculation of the renal medulla functions as a countercurrent exchanger that traps NaCl and urea deposited to the interstitium by the loops of Henle and collecting ducts, respectively. Early hypothetical descriptions of this process envisioned a system in which descending vasa recta (DVR) and ascending vasa recta (AVR) are parallel tubes that equilibrate by diffusion. According to that notion, blood flowing from the corticomedullary junction toward the papillary t...

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“…In the case of renal microvessels, where outer medullary descending vasa recta have been microdissected and perfused in vitro, osmotic water permeability driven by small solutes is very high (P f ∼0.11 cm/s) and has been attributed to transcellular water movement through AQP1 water channels (36). In response to oncotic driving forces (albumin gradients), vasa recta P f (assuming a unity albumin reflection coefficient) was ∼1 cm/s, suggesting a high paracellular water permeability involving wide pores (37). The data in this study suggest a different situation in lung microvessels, where AQP1-dependent transcellular water movement is most important.…”

Section: Figurementioning

confidence: 99%

Lung fluid transport in aquaporin-1 and aquaporin-4 knockout mice

Bai¹,

Fukuda²,

Song³

et al. 1999

J. Clin. Invest.

221

163

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Substantial quantities of fluid move across epithelial and endothelial barriers in lung. In the perinatal lung, fluid absorption from the airspaces occurs in preparation for alveolar respiration (1). In the adult lung, movement of salt and water between the airspace and capillary compartments is required for control of airspace hydration. The formation and resolution of clinical pulmonary edema involve fluid movements among the airspace, interstitial, and capillary compartments (2-4). Considerable progress has been made in understanding the molecular mechanisms of salt movement between the airspace and capillaries. Recent work has begun to define the role of the ENaC sodium channel (5), the ClC-2 and CFTR Cl -channels (6, 7), and the Na + /K + pump (8, 9).There have been recent advances in understanding the molecular mechanisms of water movement in lung. A family of (currently) 10 related molecular water channels called aquaporins has been identified in mammals (reviewed in refs. 10-12). The aquaporins are small hydrophobic membrane proteins (M r ∼30,000) with homology to the major intrinsic protein of lens fiber. Three aquaporins have been localized in lung: AQP1 in microvascular endothelia and some pneumocytes (13-15), AQP4 in the basolateral membrane of airway epithelium (16), and AQP5 in the apical membrane of type I alveolar epithelial cells (17). Aquaporin-type water channels have not yet been identified at the basolateral surface of alveolar epithelium or at the apical membrane of airway epithelia. The specific localization of aquaporins to endothelial and epithelial cells suggests a role in water movement between airspace, interstitial, and capillary compartments. Other indirect evidence supporting a physiological role for aquaporins in lung includes the increase in aquaporin expression (18)(19)(20) and lung water permeability (21) around the time of birth, and the high water permeability of alveolar (13,22), microvascular (23), and airway (24) barriers. Recently, immunopurified type I alveolar epithelial cells were found to have an exceptionally high water permeability, with biophysical properties indicative of molecular water channels (25).We have developed quantitative pleural surface fluorescence methods to measure osmotic water permeability of the airspace-capillary barrier (22) The mammalian lung expresses water channel aquaporin-1 (AQP1) in microvascular endothelia and aquaporin-4 (AQP4) in airway epithelia. To test whether these water channels facilitate fluid movement between airspace, interstitial, and capillary compartments, we measured passive and active fluid transport in AQP1 and AQP4 knockout mice. Airspace-capillary osmotic water permeability (P f ) was measured in isolated perfused lungs by a pleural surface fluorescence method. P f was remarkably reduced in AQP1 (-/-) mice These results indicate that osmotically driven water transport across microvessels in adult lung occurs by a transcellular route through AQP1 water channels and that the microvascular endothelium is a significant ba...

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Hydraulic and diffusional permeabilities of isolated outer medullary descending vasa recta from the rat

Cited by 21 publications

References 0 publications

Physiology of the renal medullary microcirculation

Physiology of the renal medullary microcirculation

Countercurrent exchange in the renal medulla

Lung fluid transport in aquaporin-1 and aquaporin-4 knockout mice

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