AJP - Renal Physiology, Vol 269, Issue 1 55-F63, Copyright © 1995 by American Physiological Society

ARTICLES

Diffusive transport of solute in the rat medullary microcirculation

T. L. Pallone, S. Nielsen, E. P. Silldorff and S. Yang
Division of Nephrology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033, USA.

Outer medullary descending vasa recta (OMDVR) permeability to sodium (PNa) is much lower than to urea (Purea). Based on these findings, we hypothesized that sodium and urea diffuse across the OMDFR wall by separate routes. To further test this, we simultaneously perfused OMDVR with 22Na and 36Cl, [14C]urea, [3H]raffinose, or tritiated water. The permeability of OMDVR to 22Na and [3H]raffinose was found to increase markedly and reversibly with perfusion rate. PNa was highly correlated with the permeability to Cl (PCl) and to [3H]raffinose (Praf) (R = 0.90 and 0.95, respectively) but not with Purea (R = 0.23). Praf was also correlated with inulin permeability (PIn) (R = 0.93). The intercepts for the regressions of PNa with PCl and Praf and for Praf with PIn were zero. In contrast, OMDVR with low PNa retained very high diffusional water permeability (PD) and Purea, a finding consistent with separate routes for permeation of those tracers. We previously established that thiourea is a competitive inhibitor of OMDVR urea transport. In the presence of 100 mM thiourea, OMDVR PNa and Purea were correlated (R = 0.71) but retained an intercept much > 0. We conclude that Na, Cl, raffinose, and inulin are likely to traverse the OMDVR wall through a common pathway, whereas specific mechanisms exist to regulate the permeation by urea and water.

This article has been cited by other articles:

				T. L. Pallone, M. R. Turner, A. Edwards, and R. L. Jamison Countercurrent exchange in the renal medulla Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2003; 284(5): R1153 - R1175. [Abstract] [Full Text] [PDF]

				T. L. Pallone, Z. Zhang, and K. Rhinehart Physiology of the renal medullary microcirculation Am J Physiol Renal Physiol, February 1, 2003; 284(2): F253 - F266. [Abstract] [Full Text] [PDF]

				J. M. Sands Molecular Approaches to Urea Transporters J. Am. Soc. Nephrol., November 1, 2002; 13(11): 2795 - 2806. [Abstract] [Full Text] [PDF]

				R. T. Timmer, J. D. Klein, S. M. Bagnasco, J. J. Doran, J. W. Verlander, R. B. Gunn, and J. M. Sands Localization of the urea transporter UT-B protein in human and rat erythrocytes and tissues Am J Physiol Cell Physiol, October 1, 2001; 281(4): C1318 - C1325. [Abstract] [Full Text] [PDF]

				J. M. SANDS Regulation of Renal Urea Transporters J. Am. Soc. Nephrol., March 1, 1999; 10(3): 635 - 646. [Abstract] [Full Text]

				S. R. Thomas Cycles and separations in a model of the renal medulla Am J Physiol Renal Physiol, November 1, 1998; 275(5): F671 - F690. [Abstract] [Full Text] [PDF]

				H. Tsukaguchi, C. Shayakul, U. V. Berger, and M. A. Hediger Urea transporters in kidney: molecular analysis and contribution to the urinary concentrating process Am J Physiol Renal Physiol, September 1, 1998; 275(3): F319 - F324. [Abstract] [Full Text] [PDF]

				X. Wang, S. R. Thomas, and A. S. Wexler Outer medullary anatomy and the urine concentrating mechanism Am J Physiol Renal Physiol, February 1, 1998; 274(2): F413 - F424. [Abstract] [Full Text] [PDF]