Increased 86Rb+ efflux from perfused rat hearts exposed to alpha 1-adrenergic stimulation.
Stimulation of myocardial alpha 1-adrenoceptors mediates changes in potassium fluxes across the sarcolemma. We studied the effect of alpha 1-adrenoceptor stimulation (5 x 10(-5) M phenylephrine with addition of 10(-6) M timolol) on potassium efflux by use of 86Rb+ efflux from isolated rat hearts perfused in a nonrecirculation system. The hearts were loaded with 86Rb+, followed by washout during which they were exposed to alpha 1-adrenergic stimulation with or without addition of the Na+/K(+)-ATPase inhibitor ouabain (10(-5) M). 86Rb+ content in perfusate fractions during the washout period and in the hearts at the end of experiments was measured; 86Rb+ efflux rates were determined as the ratio between the radioactivity of the perfusate fractions and the corresponding radioactivity contents of the hearts. alpha 1-adrenoceptor stimulation evoked a gradual increase in 86Rb+ efflux amounting to 30% of reference value after 20 min. With addition of ouabain, the alpha 1-adrenergic increase in 86Rb+ efflux developed faster and reached a maximum of approximately 40% of basal after approximately 10 min. The effects both with and without addition of ouabain were prevented by the alpha 1-adrenoceptor blocker prazosin (10(-6) M). Results indicate that increased potassium efflux is a part of alpha 1-adrenergic heart effects.
Hanem
S
S
Department of Pharmacology, University of Oslo, Norway.
Skomedal
T
T
Bjørn-Osnes
J
J
D000818:Animals; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012413:Rubidium / Q000378:metabolism*; D013999:Timolol / Q000494:pharmacology*
D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D010042:Ouabain; D013999:Timolol; D012413:Rubidium; D011188:Potassium