Monovalent ion specificity of the electrogenic sodium pump in vascular smooth muscle

Abstract

Experiments were performed to determine the monovalent ion specificity of the electrogenic sodium pump in vascular smooth muscle. Helical strips of rat tail artery relaxed in response to potassium after contraction induced by norepinephrine in potassium-free solution. This relaxation is due to the electrogenic pumping of sodium and potassium which produces membrane hyperpolarization. The magnitude of the relaxation was decreased when the strips were incubated in solutions containing low concentrations of potassium (0.01-5.0 mM) instead of zero potassium. Potassium-induced relaxation was inhibited by ouabain. Helical strips also relaxed in response to rubidium, cesium, and ammonium when these were added instead of potassium to a potassium-free solution. The effectiveness of the monovalent ions in producing relaxation was in the following order: rubidium ≥ potassium > ammonium > cesium. Ouabain inhibited the relaxation responses induced by these latter ions. The results suggest: small changes of the external potassium concentration can modify the amplitude of potassium-induced relaxation, presumably by affecting the intensity of the electrogenic pump; and rubidium, cesium, and ammonium ions can substitute for potassium in producing sodium pump electrogenicity, as evidenced by relaxation after addition of these ions and by inhibition of the relaxation in response to these ions by ouabain.