Electrophysiological effects of bunaphtine in guinea-pig ventricular fibers

The electrophysiological effects of bunaphtine (BNA) in concentrations between 10(-7) M and 10(-4) M were studied on action potential characteristics of guinea-pig ventricular fibers. In fibers stimulated at constant rate, BNA, greater or equal to 10(-5) M, did not change the resting membrane potential but significantly decreased the amplitude and maximum rate of rise of the action potential and shifted the membrane responsiveness and membrane reactivation curves downward and to the right. At concentrations greater than or equal to 10(-6) M both action potential duration and effective refractory period were prolonged. BNA also decreased ventricular excitability and maximum following frequency and suppressed the pacemaker activity induced in ventricular muscle fibers by Ba ions or by adrenaline. However, it did not modify the Ca-mediated action potentials. The mechanism responsible for the in vivo antiarrhythmic action and side effects are discussed.