Abstract

The effects of papaverine on force of contraction, action potential configuration and membrane currents were studied in ventricular heart muscle from cats. The force of contraction was variably affected by different concentrations of papaverine. At 2 X 10(-5) M papaverine, the following results were obtained. The action potential duration was prolonged at all voltage levels. The steady-state outward current and the outward tail currents after 800 msec-depolarizing voltage clamp steps were reduced. The slow inward current was slightly enhanced or reduced. Both the slow inward current and the force of contraction were greatly increased in the presence of both papaverine and isoprenaline (3 X 10(-9) M); isoprenaline (3 X 10(-9) M) alone had no significant effects either on the slow inward current or on the force of contraction. It is concluded that the predominant membrane effect of papaverine on the heart is to reduce the potassium conductance. The inhibition of papaverine on the phosphodiesterase activity does not change considerably either the slow inward current or the force of contraction. An adrenergic stimulus, however, is greatly increased in the presence of papaverine.