Comparison of the actions of saxitoxin and tetrodotoxin on the motor end‐plate of frog muscle

End-plate potentials (e.p.p.) and responses to ionophoretic application of acetylcholine (ACh potentials) have been recorded in frog muscle. Saxitoxin (STX) and tetrodotoxin (TTX) abolished the e.p.p. at concentrations of 10(-8) g/ml. In almost all cases there was no effect on the ACh potentials even when the concentrations were raised, STX to 1.2 x 10(-6) g/ml (3.2 x 1O(-6)M), or TTX to 5 x 10(-6) g/ml (1.5 x 10(-5)M). STX, 10(-6) g/ml (2.7 x 10(-6)M) often caused a slow rise in the frequency of miniature e.p.p., without significant effect on amplitude.