Effects of ATP on Na+ transport and membrane potential in inside-out renal basolateral vesicles.

We have studied Na+ transport in inside-out basolateral membrane vesicles isolated from rabbit kidney cortex. The addition of ATP in the presence of Mg2+ to the outside of K+-loaded vesicles induced a rapid influx of Na+ against its chemical gradient. Whereas intravesicular K+ was required, extravesicular K+ was inhibitory. ATP-dependent Na+ uptake was inhibited by intravesicular, but not extravesicular ouabain, while extravesicular vanadate was inhibitory. Evaluation of changes in membrane potential using the lipophilic cation triphenylmethylphosphonium (TPMP+) demonstrated hyperpolarization of the membrane voltage after MgATP addition. Changing membrane potential from zero to -40 mV had no effect on ATP-dependent Na+ transport. The potential produced MgATP was inhibited by valinomycin and by protoinophores, but not by vanadate or ouabain. By contrast, the hyperpolarization that occurred in mitochondria after MgATP addition was inhibited by 75% by vanadate. We conclude that the properties of the renal basolateral sodium pump are qualitatively similar to those found in red cell and nerve and that these membranes probably also contain an electrogenic proton pump.