Beta-adrenergic induced potassium current in Xenopus oocyte: involvement of cyclic AMP.

The effect of a beta-adrenergic agonist, on full-grown Xenopus oocytes, still surrounded by their ovarian envelopes, has been studied by electrophysiological methods. The oocytes were hyperpolarized by isoproterenol. Under voltage clamp, the elicited outward current reversed at a membrane potential of - 95 mV, a value close to the K+ equilibrium potential. The isoproterenol induced current varied linearly with the membrane potential in the range studied (- 120 mV, - 30 mV). Half-maximum current was obtained at 3.10(-8) M isoproterenol. Propranolol (10(-7) M) completely suppressed the response to isoproterenol (10(-9) to 10(-5) M). 8-Br-cAMP induced a current which also reversed at - 95 mV. Methyl-isobutyl-xanthine (MIX), a potent inhibitor of phosphodiesterases, potentiated the current induced by isoproterenol. These experiments strongly suggest that the increase in K+ permeability due to catecholamines is mediated by cAMP.