Influence of transmembrane potential differences of renal tubular epithelial cell on ANG II binding

Abstract

Previous studies from this laboratory demonstrated specific high-affinity binding sites of rat renal brush-border membrane vesicles (BBMV). The time course of angiotensin II (ANG II) binding in the presence of a NaCl gradient (medium greater than intravesicular) demonstrated an "overshoot" characteristic of electrogenic sodium-dependent D-glucose uptake. The time course of ANG II binding to membrane vesicles equilibrated with NaCl did not exhibit such "overshoot" and was lower in magnitude. Therefore, studies were designed to test the hypothesis that ANG II binding to BBMV was enhanced by a transmembrane potential difference in a manner similar to sodium-dependent D-glucose uptake. The effects of sodium salts with differing rates of anion equilibration were compared on ANG II binding. Peak binding was achieved most rapidly with NaSCN followed by NaCl and Na2SO4. By contrast, sodium acetate, which is translocated electroneutrally, exhibited no overshoot. ANG II binding in the presence of a KCl gradient was similar to NaCl. The overshoot was abolished in the presence of an inwardly directed KCl gradient plus valinomycin. Magnesium salts with differing rates of anion permeabilities had similar effects on binding, as did sodium salts. Scatchard analysis revealed that the receptor density was fourfold higher in the presence of an electrochemical gradient compared with nongradient conditions. These data are consistent with the conclusion that ANG II binding to BBMV is enhanced by a transmembrane potential difference, and suggest that this may be an important modulator of tubular epithelial responses to ANG II in vivo.