Diffusive transport of solute in the rat medullary
microcirculation.
Pallone, Thomas L., Soren Nielsen, Erik P. Silldorff, and Sai Yang.
Division of Nephrology, The M.S. Hershey Medical Center of the
Pennsylvania State University, Hershey, PA and the Department of Cell
Biology, Institute of Anatomy, University of Aarhus, Aarhus,
Denmark
APStracts 2:0023F, 1995.
Diffusive transport of solute in the rat medullary microcirculation.
Outer medullary descending vasa recta (OMDVR) permeability to sodium
(Pna) is much lower than to urea (Pu). Based on these findings, we
hypothesized that sodium and urea diffuse across the OMDVR wall by
separate routes. To further test this, we simultaneously perfused
OMDVR with 22Na and 36Cl, 14Curea, 3Hraffinose, or tritiated water
(THO). The permeability of OMDVR to 22Na and 3Hraffinose was found to
increase markedly and reversibly with perfusion rate. Pna was highly
correlated with PCl, and PRAF, (R=0.90, 0.95, respectively) but not
with Pu (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 Pu, a
finding which is 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 Pu was correlated (R=0.71) but retained an
intercept much greater than zero. We conclude that Na, Cl, raffinose
and inulin are likely to traverse the OMDVR wall through a common
pathway while specific mechanisms exist to regulate the permeation by
urea and water.
Received 30 September 1994; accepted in final form 14 February
1995.
APS Manuscript Number F349-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 1 March 1995.