Abstract

The effects of neuromuscular blocking concentrations of hexamethonium and decamethonium on end-plate current parameters have been studied in frog sartorius nerve-muscle preparations. In the presence of either drug, hyperpolarization of the cell membrane reduces the peak amplitude of the end-plate current despite the increase in driving force. The effect is larger for hexamethonium than for decamethonium. In the presence of decamethonium, hyperpolarization reduces the time to peak of the end-plate current and splits the decay phase into two components, one faster and the other slower than in controls. Similar but less dramatic effects on parameters of end-plate current shape occur in the presence of hexamethonium. For both drugs, the decay of the end-plate current can be fitted by the sum of two exponential functions. Hyperpolarization speeds the initial fast component and slows the subsequent slow component. These results are consistent with the hypothesis that both drugs act in part by direct block of open ion channels.