[Effect of calcium channel blockaders (verapamil, D-600 and manganese ions) on mediator release from frog muscle motor nerve endings]

Abstract

The reduction in the EPPs quantum content produced by manganese ions (0.4-5.0 mM) was observed in the frog sartorius muscle. In contrast to the inhibitory action on the evoked release, manganese ions increased a spontaneous transmitter release. Verapamil (1-10(-6)-5-10(-5) g/ml) and D-600 (2.5-10(-5) g/ml) did not inhibit the evoked release but increased the spontaneous one. All the calcium antagonists studied were able to prevent the facilitatory effect of imidazole (3 mM) on neuromuscular transmission. Verapamil (5-10(-6)-5-10(-5) g/ml) disturbed the action potential generation during the repetitive stimulation of the motor nerve. Manganese ions were ineffective in this respect. A conclusion is made that the calcium ionic channels in the nerve terminals differ from the calcium channels in some other tissues (heart, soma of neurons etc.).