Abstract
The active phase (end-plate current) of the end-plate potential, and the relationship between the amplitude of the end-plate potential or the end-plate current and the membrane polarization produced by passing current across the muscle membrane were studied in frog sciatic nerve-sartorius treated with PG (phenethylguanidine), which seems to have both competitive and noncompetitive receptor-blocking actions. The falling phase of the end-plate current in PG was slightly but clearly prolonged as compared with that in dTc, a typical competitive receptor blocking agent. The equilbirium potential obtained by the collision experiment (del Castillo and Katz 1954) in PG was found to be at about -15 mV, suggesting that PG did not influence significantly the ratio PNa/PK raised by ACh at the end-plate membrane. However, the equilibrium potential was not determined by membrane polarization produced by passing the current across the membrane. Amplitudes of both end-plate potential and end-plate current were increased with muscle membrane depolarization and were decreased with hyperpolarization. Possible factors which may account for these relationships are discussed.
