Membrane potential and reactivity to potassium of duodenal smooth muscle from spontaneously hypertensive rats.

Na/K-ATPase from the duodenum of spontaneously hypertensive rats (SHR) is inhibited compared to that of the Wistar-Kyoto (WKY) controls. The present study investigates depolarization of smooth muscle cell membranes through direct determination of the membrane potential in the longitudinal duodenal smooth muscle isolated from the two rat strains. Membrane potentials were not different in the two groups: -64.0 +/- 0.5 mV (N = 86) (means +/- SEM) in SHR and -62.0 +/- 3.0 mV (N = 95) in the WKY group. However, when the electrogenic contribution of Na/K-ATPase was abolished by removing potassium from the extracellular medium, the membrane potentials differed significantly: -35.0 +/- 1.0 mV (N = 45) and -28.0 +/- 1.0 mV (N = 48) for SHR and WKY, respectively. The lower depolarization observed in the duodena isolated from SHR is a further indication that the sodium pump is inhibited in these animals.