[Effect of calcium antagonists on action potentials of muscle fibers in the warm-blooded].

The effect of the "calcium antagonist" D600 (5.10(-6)--1.10(-4) g/ml) on the amplitude, duration and rate of the rise (Vmax) on the action potential (AP) of mouse diaphragm muscle fibers were studied. To evoke and record the AP, a standard microelectrode technique was employed with two microelectrodes being inserted into the same fiber about 50 micrometer apart. The fibers were stimulated by a single pulse or by serial ones. D600 was shown to reduce the amplitude and Vmax of AP and to increase its duration both in innervated and denervated muscle fibers. The magnitude of the membrane potential and the input resistance were not affected by D600. After denervation the sensitivity of muscle fibers to D600 fell. In the course of stimulation applied by serial pulses (1--2 Hz) instead of single ones, the inhibitory effect of D600 drastically increased. It is suggested that D600 strongly modifies the activity of fast sodium channels, the manifestations of the effect being controlled by innervation.