AJP - Renal Physiology, Vol 259, Issue 6 986-F999, Copyright © 1990 by American Physiological Society
Water permeability of apical and basolateral cell membranes of rat inner medullary collecting duct
B. Flamion and K. R. Spring
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
To quantify the pathways for water permeation through the kidney medulla,
knowledge of the water permeability (Posmol) of individual cell membranes
in inner medullary collecting duct (IMCD) is required. Therefore IMCD
segments from the inner two thirds of inner medulla of Sprague-Dawley rats
were perfused in vitro using a setup devised for rapid bath and luminal
fluid exchanges (half time, t1/2, of 55 and 41 ms). Differential
interference contrast microscopy, coupled to video recording, was used to
measure volume and approximate surface areas of single cells. Volume and
volume-to-surface area ratio of IMCD cells were strongly correlated with
their position along the inner medullary axis. Transmembrane water flow
(Jv) was measured in response to a variety of osmotic gradients (delta II)
presented on either basolateral or luminal side of the cells. The linear
relation between Jv and delta II yielded the cell membrane Posmol, which
was then corrected for membrane infoldings. Basolateral membrane Posmol was
126 +/- 3 microns/s. Apical membrane Posmol rose from a basal value of 26
+/- 3 microns/s to 99 +/- 5 microns/s in presence of antidiuretic hormone
(ADH). Because of amplification of basolateral membrane, the ADH-stimulated
apical membrane remained rate-limiting for transcellular osmotic water
flow, and the IMCD cell did not swell significantly. Calculated
transcellular Posmol, expressed in terms of smooth luminal surface, was 64
microns/s without ADH and 207 microns/s with ADH. IMCD cells in anisosmotic
media displayed almost complete volume regulatory decrease but only partial
volume regulatory increase.
