Abstract
Summary: Stimulation of myocardial α1-adrenoceptors has been shown to mediate various changes in potassium fluxes across the sarcolemma. We studied the early effect of α1-adrenoceptor stimulation [5 × 10−5M phenylephrine (PE) with 10−6M timolol] on potassium influx by measuring uptake of 86Rb+ into isolated rat heart perfused in a nonrecirculating system. The hearts were exposed to α1-adrenoceptor stimulation with or without the Na+/K+-ATPase inhibitor ouabain (10−5M) 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. α1-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 α1-adrenoceptor antagonist prazosin (10−6M) prevented the effects of PE. Therefore, increase in potassium influx is mediated by α1-adrenoceptors.
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