Membrane Effects of Pronethalol on the Mammalian Heart Muscle Fiber

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Abstract
Pronethalol decreased the pacemaker activity of the ventricle (right bundle branch of dog) and of the sinus node (rabbit). Conduction velocity, critical membrane potential and maximumdepolarization rate were all reduced by pronethalol. Absolute and relative refractory period were prolonged, and Na-inactivation curve shifted to the right (inhibition of Na-carrier system) by pronethalol, whereas no or little effects, if any, were observed on the resting potential and membrane resistance in resting and acting phases. The mechanism of antiarrhythmic action of pronethalol was discussed, and it was concluded that the mechanism is not the same as that for the well-known beta-blocking of pronethalol.