Transport of sodium and urea in outer medullary descending vasa recta.

Pallone, Thomas L.; Work, Jack; Myers, Roland L.; Jamison, Rex L.

doi:10.1172/jci116948

Cited by 86 publications

(93 citation statements)

References 37 publications

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“…No constriction occurred during progressive luminal pressure elevation. This reinforces prior observations that were obtained under free-flow conditions (30,33).…”

Section: Dvr Endothelial Ca 2ϩ Responses To Free-flow Microperfusionsupporting

confidence: 91%

“…DVR are ϳ13-15 m in outer diameter requiring pipette tips typically ϳ5-m internal diameter ϫ 500 m long to achieve cannulation. Collecting pipettes with small openings are needed to anchor DVR during microperfusion and seal the collectate from the bath so that accurate timed collections of effluent flow rate can be obtained (30,33). In addition to constriction of the vessel outlet by the collection pipette, adherence of the extracellular matrix at the cut end across the opening often partially blocks outflow.…”

Section: Discussionmentioning

confidence: 99%

“…DVR were dissected from outer medullary vascular bundles and transferred to the stage of an inverted microscope as previously described (30,33). Vessels were mounted on concentric pipettes, cannulated at one end, and held at the other end in a manner that either permitted free flow into the collection pipette or crimped the end to enable pressurization of the lumen without flow (Fig.…”

Section: Isolation and Microperfusion Of Dvrmentioning

confidence: 99%

“…Their radial distribution within vascular bundles implies that they distribute and regulate regional blood flow within the medulla (34). DVR are lined with a continuous endothelium and enveloped by smooth muscle/pericytes that impart contractility (30,33). The importance of endothelial secretion of paracrine mediators to modulate adjacent smooth muscle is well established.…”

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confidence: 99%

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Response of descending vasa recta to luminal pressure

Zhang¹,

Pallone²

2004

American Journal of Physiology-Renal Physiology

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Zhang, Zhong, and Thomas L. Pallone. Response of descending vasa recta to luminal pressure. Am J Physiol Renal Physiol 287: F535-F542, 2004. First published May 4, 2004 10.1152/ajprenal. 00394.2003.-We tested whether luminal perfusion and pressurization induce an endothelial cytoplasmic Ca 2ϩ ([Ca 2ϩ ]CYT) response in descending vasa recta (DVR). DVR isolated from the rat outer medulla were cannulated and subjected to free-flow microperfusion (5 nl/min); the onset of which increased [Ca 2ϩ ]CYT from a baseline of 76 Ϯ 13 to 221 Ϯ 65 nM. A graded increase in luminal pressure from 0 to 45 mmHg in stopped-flow experiments induced a parallel increase in [Ca 2ϩ ]CYT from a baseline of 74 Ϯ 24 to 194 Ϯ 33 nM at 45 mmHg, with a tendency for [Ca 2ϩ ]CYT to plateau at pressures Ͼ25 mmHg. The removal of extracellular Ca 2ϩ and blockade by either La 3ϩ (10 M) or SKF-96365 (100 M) eliminated the response. Luminal pressurization to 25 mmHg increased nitric oxide (NO) generation, a response blocked by NO synthase inhibition or removal of extracellular Ca 2ϩ . The NO generation was not affected by the superoxide dismutase mimetic tempol. We conclude that DVR endothelia are mechanosensitive and respond to luminal pressure by elevating [Ca 2ϩ ]CYT and generating NO. That response might augment medullary perfusion and saliuresis. medulla; kidney; microcirculation; shear; fura 2; 4,5-diaminofluoroscein DESCENDING VASA RECTA (DVR) are small generation resistance vessels that carry blood flow from the cortex to the medulla of the kidney. They originate as branches of the juxtamedullary efferent arteriole and traverse the outer medulla in vascular bundles to supply the inner and outer medulla. Their radial distribution within vascular bundles implies that they distribute and regulate regional blood flow within the medulla (34). DVR are lined with a continuous endothelium and enveloped by smooth muscle/pericytes that impart contractility (30,33). The importance of endothelial secretion of paracrine mediators to modulate adjacent smooth muscle is well established. Motivated by the importance of nitric oxide (NO) secretion in the maintenance of renal medullary perfusion and blood pressure (7,22,23,28) we employed microperfusion and fluorescence microscopy to test whether DVR endothelial cytoplasmic Ca 2ϩ ([Ca 2ϩ ] CYT ) is affected by the transmural pressure gradient imposed across the DVR wall. We exploited the property of the Ca 2ϩ -sensitive probe, fura 2, to preferentially load into DVR endothelia (while sparing pericytes) to quantify the effect of raising intraluminal pressure on [Ca 2ϩ ] CYT . In addition, the probe 4,5-diaminofluorescein (DAF-2), which increases fluorescence when covalently modified by NO, was used to monitor NO generation. The results verify that an increase in luminal pressure is accompanied by a parallel rise in DVR endothelial [Ca 2ϩ ] CYT and a robust increase in NO synthesis.NO functions as a vasodilator and "endogenous diuretic" (23, 28). We hypothesize that the vasa recta endothelium might serve a...

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“…No constriction occurred during progressive luminal pressure elevation. This reinforces prior observations that were obtained under free-flow conditions (30,33).…”

Section: Dvr Endothelial Ca 2ϩ Responses To Free-flow Microperfusionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Isolation and Microperfusion Of Dvrmentioning

confidence: 99%

mentioning

confidence: 99%

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Response of descending vasa recta to luminal pressure

Zhang¹,

Pallone²

2004

American Journal of Physiology-Renal Physiology

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“…Near their termination, DVR become fenestrated and give rise to a sparse capillary plexus. The plexus coalesces to form AVR that are characterized by a high degree of fenestration (117,138). The fraction of the AVR wall occupied by fenestrations is larger in the inner medulla than in the outer medulla.…”

Section: Renal Medullary Microvascular Anatomymentioning

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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Microvessel Permeability

2006

Wiley Encyclopedia of Biomedical Engineering

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Microvessel permeability is a quantitative measure of how permeable the microvessel wall is to all kinds of substances including water, solutes, and cells. Important and recent progresses in microvessel permeability and its regulation are presented and discussed. Although microvessel permeability is a classic problem that has been investigated for more than 50 years, the fundamental question related to structure‐function of microvessel walls and properties of cells forming the walls still remains unclear. Employing mathematical models for more accurate interpretations and predictions, new techniques involving fluorescence, atomic force and electron microscopy, and new developments in molecular biology and biochemistry will lead to more fascinating discoveries in this field.

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Transport of sodium and urea in outer medullary descending vasa recta.

Cited by 86 publications

References 37 publications

Response of descending vasa recta to luminal pressure

Response of descending vasa recta to luminal pressure

Physiology of the renal medullary microcirculation

Microvessel Permeability

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