AJP - Cell Physiology, Vol 256, Issue 2 C304-C309, Copyright © 1989 by American Physiological Society
Effects of charge on membrane processing in the proximal nephron
D. R. Peterson, S. Kubillus, W. Binstock and D. Zikos
Department of Physiology and Biophysics, University of Health Sciences, Chicago Medical School, Illinois 60064.
To examine the effects of molecular charge on membrane processing in renal
tubular cells, the distribution of cationic and anionic ferritin was
characterized in microperfused proximal nephron segments. During the first
7 min of proximal tubule perfusion, cationic ferritin was observed 1) bound
to the brush-border membrane, 2) in apically positioned vesicles and
vacuoles, 3) in lysosomes, 4) in vesicles adjacent to the basolateral
plasmalemma, and 5) bound to the basolateral plasmalemma. Compared with
anionic ferritin, the distribution of cationic ferritin was characterized
by 1) a smaller relative grain density for lysosomes, 2) an accumulation of
granules in an enlarged pool of apical cytoplasmic vesicles and vacuoles,
and 3) a greater number of granules reaching the basolateral plasmalemma.
During incubation directly in the presence of isolated renal cortical
microvilli, binding of cationic ferritin increased significantly as pH was
lowered from 8.0 to 4.5 and was greater than that of anionic ferritin,
which varied little with pH. The data indicate that the molecular charge of
endocytosed substances affects routing and membrane processing in proximal
tubular cells, suggesting that their membrane-binding characteristics may
influence transport patterns.
