EFFECTS OF PAPAVERINE ON CA++-DEPENDENT ACTION-POTENTIALS IN GUINEA-PIG MYOCARDIUM DEPOLARIZED BY POTASSIUM

  • 1 January 1981
    • journal article
    • research article
    • Vol. 219  (3) , 715-722
Abstract
Ventricular and atrial tissues isolated from guinea-pig hearts were depolarized by exposure to 22 mM K+ to study the effects of papaverine on the Ca2+-mediated slow inward current (ISi). Papaverine at 5 .times. 10-6-5 .times. 10-5 M caused a concentration-dependent decrease in the threshold current required to excite the field-stimulated tissues and an enhancement of action potential amplitude, action potential duration and maximum rate of depolarization of the Ca2+-dependent action potentials. In ventricular preparations, 5 .times. 10-5 and 10-4 M papaverine invariably induced rhythmic spontaneous activity that was abolished by verapamil. The membranal electrical effects of papaverine in the K+-depolarized myocardium are caused by an enhancement of ISi and a decrease in K+ conductance. At the highest concentration studied (10-4 M), papaverine inhibited ISi in atrial tissue, demonstrating that papaverine exerts another action on ISi opposite to that observed at lower concentrations.

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