AJP - Renal Physiology, Vol 244, Issue 6 686-F695, Copyright © 1983 by American Physiological Society
Citrate uptake by basolateral and luminal membrane vesicles from rabbit kidney cortex
K. E. Jorgensen, U. Kragh-Hansen, H. Roigaard-Petersen and M. I. Sheikh
The mechanisms of tubular transport of citrate in renal basolateral and
luminal membrane vesicles were studied under various experimental
conditions. Both membrane preparations take up citrate by a Na+-dependent
transport system, although with different characteristics. The uptake of
citrate by basolateral membrane vesicles was insensitive to changes in
membrane potential, which is indicative of electroneutral transport of the
anion. The Na+-dependent uptake of citrate by luminal membrane vesicles was
influenced by the presence of Na+salt anions of different permeabilities in
the order: chloride greater than sulfate greater than gluconate.
Furthermore, addition of citrate to membrane vesicle-potential-sensitive
dye suspensions resulted in optical changes of the dye, indicative of
electrogenic transfer of this compound. The apparent affinity of the
citrate transport system located in luminal membrane vesicles, in contrast
to basolateral membrane vesicles, was sensitive to changes in medium pH and
was higher than that of basolateral membrane vesicles in the pH range
studied. On the basis of these results a model for the transport of citrate
by rabbit kidney proximal tubule is proposed.
