Alpha 1-adrenoceptor stimulation increases 86Rb+ influx in perfused rat heart

Stimulation of myocardial alpha 1-adrenoceptors has been shown to mediate various changes in potassium fluxes across the sarcolemma. We studied the early effect of alpha 1-adrenoceptor stimulation [5 x 10(-5) M phenylephrine (PE) with 10(-6) M timolol] on potassium influx by measuring uptake of 86Rb+ into isolated rat heart perfused in a nonrecirculating system. The hearts were exposed to alpha 1-adrenoceptor stimulation with or without the Na+/K(+)-ATPase inhibitor ouabain (10(-5) M) during the influx period of 86Rb+ and during the subsequent washout period. 86Rb+ content in the perfusate fractions during the washout period and in heart at the end of experiments were measured. From these data, 86Rb+ content in heart after 2.5, 5.5, and 9.5 min was calculated. alpha 1-adrenoceptor stimulation increased 86Rb+ uptake by 20-40% during the observation period. The influence of ouabain did not indicate clear-cut involvement of Na+/K(+)-ATPase in this effect. The alpha 1-adrenoceptor antagonist prazosin (10(-6) M) prevented the effects of PE. Therefore, increase in potassium influx is mediated by alpha 1-adrenoceptors.