AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 1 186-R191, Copyright © 1991 by American Physiological Society
Axial heterogeneity of apical water permeability along rabbit kidney proximal tubule
F. Van Der Goot and B. Corman
Departement de Biologie, Centre d'Etudes Nucleaires de Saclay, Gif-sur-Yvette, France.
In the rabbit nephron, the luminal membrane surface area of the proximal
convoluted tubule (PCT) is more than twice that of the proximal straight
tubule (PST). What seemed to be an increase in histological specialization
in solute and water transport is curiously reflected by a lower
transepithelial water permeability per unit of apical membrane area in PCT
than in PST. To evaluate what change in luminal membrane water permeability
corresponds to this morphological difference, the osmotic permeabilities
(Pf) of brush-border membrane vesicles isolated from PCT and PST of rabbit
kidney were compared. D-Glucose uptake rates indicated proper separation of
two populations of vesicles. Vesicle size measured by quasi-elastic light
scattering was 123 +/- 7 nm and 125 +/- 6 nm for vesicles isolated from PCT
and PST, respectively. Pf obtained by stop-flow light scattering techniques
was of 106 +/- 6 microns/s in PCT vesicles and 191 +/- 7 microns/s in PST
vesicles (T = 26 degrees C). In the presence of the sulfhydryl reagent
HgCl2, the water permeabilities of both types of membrane dropped to
comparable values. These data, which show an 80% increase in apical water
permeability along the length of the proximal tubule, suggest that the
number of proteic water channels per unit of membrane area is greater in
PST than in PCT.
