[Effects of nizofenone on the action potential of guinea-pig papillary muscle and S-A node and dog Purkinje fibers]

Effects of nizofenone, an agent which has been known to have a protective effect against experimental cerebral ischemia or anoxia, on the action potential of guinea-pig papillary muscle and S-A node and dog Purkinje fibers were studied. Nizofenone (10(-6) and 10(-5) M) significantly prolonged the action potential duration of guinea-pig papillary muscle and dog Purkinje fibers accompanying prolongation of the effective refractory period in dog Purkinje fibers. Nizofenone decreased Vmax at the concentrations of 10(-5) and 10(-4) M in guinea-pig papillary muscle and at 10(-4) M in dog Purkinje fibers. Nizofenone suppressed the spontaneous activity of dog Purkinje fibers and guinea-pigs S-A node at the concentrations of 3 X 10(-5) to 10(-4) M and 10(-5) M, respectively. Nizofenone (10(-4) M) decreased the contractile force of guinea-pig papillary muscle. In the guinea-pig papillary muscle, the effect of nizofenone on action potential duration was almost the same as that of quinidine, but the inhibitory effect on Vmax was slightly weaker than quinidine. These results suggest that nizofenone has a so-called "quinidine-like action" on cardiac membrane.