ALPHA(1)-ADRENOCEPTOR STIMULATION INCREASES RB-86(+) 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 Rb-86(+) 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 Rb-86(+) and during the subsequent washout period, Rb-86(+) content in the perfusate fractions during the washout period and in heart at the end of experiments were measured. From these data, Rb-86(+) content in heart after 2.5, 5.5, and 9.5 min was calculated. alpha(1)- adrenoceptor stimulation increased Rb-86(+) 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.