Key result
Pronethalol depressed pacemaker activity, prolonged the refractory period, and depressed conduction velocity by inhibiting the active inward current carrier system.
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Pronethalol's antiarrhythmic action is primarily due to the depression of the active inward current (Na-carrier system) rather than its beta-blocking properties.
Actions of pronethalol on the electrophysiological properties of the mammalian heart muscle were investigated. 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 maximum depolarization 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 wellknown beta-blocking action of pronethalol.
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Shigenobu et al. (1966) studied Normal cardiac muscle fibers. Pronethalol vs. Control (Tyrode's solution) was evaluated on Electrophysiological properties (pacemaker activity, refractory period, conduction velocity). Pronethalol depressed pacemaker activity, prolonged the refractory period, and depressed conduction velocity by inhibiting the active inward current carrier system.
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