AJP - Renal Physiology, Vol 249, Issue 3 338-F345, Copyright © 1985 by American Physiological Society
Na+ gradient-dependent glycine uptake in basolateral membrane vesicles from the dog kidney
S. J. Schwab and M. R. Hammerman
The imposition of a Na+ gradient (extravesicular greater than
intravesicular) stimulated the uptake of [3H]glycine measured over time in
basolateral membrane vesicles from dog kidney over that measured in the
presence of a choline+ gradient or measured under Na+-equilibrated
conditions. Na+ gradient-dependent uptake of [3H]glycine was stimulated by
an intravesicular-negative membrane potential. Efflux of [3H]glycine was
enhanced by an intravesicular-positive membrane potential. Substrate
velocity analysis of net Na+-dependent [3H]glycine uptake over the range of
amino acid concentrations from 10 to 500 microM demonstrated a single
saturable transport system with apparent Km = 84 microM and apparent Vmax =
143 pmol [3H]glycine X mg protein-1 X 15 s-1. Counterflow of [3H]glycine
was demonstrated in the presence of Na+ when basolateral vesicles were
preloaded with glycine but not with L-alanine or L-proline. These findings
are consistent with carrier-mediated, electrogenic cotransport of Na+ and
glycine in basolateral vesicles. Unlike the case for [3H]glycine, Na+
gradient-dependent uptake of neither L-[3H]alanine nor L-[3H]proline was
observed in basolateral vesicles. Na+ gradient-dependent uptake of all
three amino acids was demonstrated in brush border vesicles from the dog
kidney. We conclude that variability exists between basolateral and brush
border membranes in terms of the presence or absence of Na+-dependent
transport systems for specific amino acids. This variability probably
reflects differences between the functional significances of the
Na+-dependent transport processes in the two membranes.
