AJP - Renal Physiology, Vol 252, Issue 6 1129-F1147, Copyright © 1987 by American Physiological Society
Isolated perfused Ambystoma proximal tubule: hydrodynamics modulates ultrastructure
S. Tripathi, E. L. Boulpaep and A. B. Maunsbach
A method using a pressure-sensing servo-pipette is described for measuring
downstream transepithelial pressure within isolated renal tubules perfused
at flow rates designed to keep luminal solution composition constant. The
hydrodynamics of in vitro microperfusion of isolated proximal tubules of
Ambystoma tigrinum was varied and different states of transepithelial
hydrostatic pressure difference, axial tubule flow, and transepithelial
transport were correlated with epithelial ultrastructure. Tubules analyzed
by ultrastructural morphometry were as follows: unperfused with and without
ouabain, perfused single-end cannulated with and without ouabain, and
perfused double-end cannulated tubules incubated in substrate Ringer. The
results indicate that proximal tubule fine structure is well preserved for
more than 3 h in unperfused and perfused tubules. Small transepithelial
hydrostatic pressure gradients (less than 162 Pa) increase tubule diameters
and decrease cell height without changing volumes of the cells, lateral
intercellular spaces (LIS), or the basal extracellular labyrinth (BEL).
Pressure gradients of 271 Pa have no further effect on tubule diameters or
cell height, but significantly reduce volumes of LIS and BEL. Transport
inhibition and axial flow changes have minor structural effects. This study
demonstrates a close dependence of tubule ultrastructure on hydrodynamic
conditions and provides guidelines for optimizing the latter during
perfusion of isolated renal tubules.
