Dicarboxylate transport in renal basolateral and brush-border membrane vesicles

Abstract

Characteristics of succinate transport were determined in basolateral and brush-border membrane vesicles (BLMV and BBMV, respectively) isolated in parallel from rabbit renal cortex. The uptake of succinate was markedly stimulated by the imposition of an inwardly directed Na+ gradient, showing an "overshoot" phenomenon in both membrane preparations. The stimulation of succinate uptake by an inwardly directed Na+ gradient was not significantly affected by pH clamp or inhibition of Na+–H+ exchange. The Na+-dependent and -independent succinate uptakes were not stimulated by an outwardly directed pH gradient. The Na dependence of succinate uptake exhibited sigmoidal kinetics, with Hill coefficients of 2.17 and 2.38 in BLMV and BBMV, respectively. The Na+-dependent succinate uptake by BLMV and BBMV was stimulated by a valinomycin-induced inside-negative potential. The Na+-dependent succinate uptake by BLMV and BBMV followed a simple Michaelis–Menten kinetics, with an apparent Km of 22.20 ± 4.08 and 71.52 ± 0.14 μM and a Vmax of 39.0 ± 3.72 and 70.20 ± 0.96 nmol/(mg·min), respectively. The substrate specificity and the inhibitor sensitivity of the succinate transport system appeared to be very similar in both membranes. These results indicate that both the renal brush-border and basolateral membranes possess the Na+-dependent dicarboxylate transport system with very similar properties but with different substrate affinity and transport capacity.Key words: dicarboxylate transport, brush border membrane, basolateral membrane, inhibitors, rabbit kidney.