Inhibition by isoproterenol of the passive potassium efflux from pigeon erythrocytes.

Pigeon erythrocytes were carefully washed in an isotonic neutral buffer, devoid of potassium, and the rate of passive unidirectional efflux of potassium from the cells into a K+-free medium was measured after 20 min, at 40 degrees C. Isoproterenol inhibits K+-efflux by 35-45%, at a cell concentration of 1%; the isoproterenol effect is mediated by beta-adrenergic receptors. Cyclic AMP mimics the effect of isoproterenol, but at 4-5 orders of magnitude higher concentrations. Cyclic AMP increases 20-fold the phosphorylation of purified cell membranes by [gamma 32P]ATP.