THE ACTION OF THE SODIUM IONOPHORE, MONENSIN, ON TRANSMITTER RELEASE AT THE FROG NEUROMUSCULAR-JUNCTION

The action of the Na ionophore, monensin, on spontaneous and evoked transmitter release at the frog neuromuscular junction was studied. Ringer''s solutions with low Ca concentrations (0.4 mM or 0 Ca 1 mM EGTA [ethyleneglycol-bis(beta-aminoethyl ether)N,N,N''N''-tetraacetic acid]) were used to bathe the preparation. Following addition of monensin to the bathing solution: substantial increases in miniature end-plate potential frequency occurred; tetanic nerve stimulation caused increases in potentiation of approximately 10 times over control values and there was a dual action on the amplitude of the end-plate potential. Na+ evidently take part in the regulation of transmitter release at the neuromuscular junction.