AJP - Renal Physiology, Vol 256, Issue 1 18-F28, Copyright © 1989 by American Physiological Society
Differential permeabilities of rat renal brush-border and basolateral membrane vesicles
M. S. Lipkowitz and R. G. Abramson
Department of Medicine, Mount Sinai School of Medicine, New York, New York 10029.
Potassium chloride permeability and relative ionic conductances of rat
renal cortical brush-border (BBMV) and basolateral (BLMV) membrane vesicles
were examined using the fluorescent probe 3,3'-dipropylthiadicarbocyanine
iodide [diS-C3-(5)]. Vesicles were simultaneously isolated and separated by
free-flow electrophoresis. These studies demonstrated that neither BBMV nor
BLMV equilibrated in 100 mM KCl despite prolonged incubation. In both, an
inwardly directed KCl gradient was sustained for 3 h. The low
intravesicular KCl concentration of BLMV was confirmed utilizing the
response of electrogenic Na+-dependent [3H]glutamine transport to
variations in the membrane potential. Chloride conductance was
significantly less than potassium conductance in BBMV and BLMV.
Consequently, an inside-positive potential was maintained across both
membranes. BLMV were significantly more fluid, less permeable, had a lower
relative chloride conductance, and maintained a greater inside-positive
potential than BBMV. The KCl permeabilities of BBMV and BLMV were inversely
related to endogenous membrane copper content and were significantly
reduced by exogenous copper. Permeability did not correlate with membrane
magnesium content, nor was it affected by exogenous magnesium. These
studies suggest that endogenous copper as well as intracellular factors may
regulate the permeabilities of the brush-border and basolateral membranes
of proximal tubule cells in vivo.
