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At the neuromuscular junction calcium and magnesium ions play an essential role (KUFFLER, 1944; DEL CASTILLO and STARK, 1952; DEL CASTILLO and ENGBAEK, 1954; BOYD and MARTIN, 1956; HUBBARD, JONES and LANDAU, 1968). These ions influence the frequency of the miniature end-plate potentials (m. e. p. p. s.) in mammalian preparations but no consistent effect has been detected in amphibian muscles (FATT and KATZ, 1952; DEL CASTILLO and KATZ, 1954; HUBBARD, 1961). It has been shown that alcohols increase the amplitude of the end-plate potentials (e. p. p. s) and also increase the frequency and the amplitude of m. e. p. p. s in amphibian and mammalian muscles (GAGE, 1965; OKADA, 1967a). It has been found recently that in amphibian muscles the frequency of m. e. p. p. s is accelerated, furthermore, when the concentration of calcium is raised in alcohol-Ringer's solution and magnesium acts as an antagonist to calcium. This result has already been briefly reported (OKADA, 1967b). In the present experiment it is shown that calcium, strontium and barium ions affect the frequency of m. e. p. p. s in amphibian muscles in the presence of ethanol and magnesium ion acts as an antagonist to these divalent cations. The fact that calcium and magnesium ions act on the amplitude of e. p. p. s but not on the frequency of m. e. p. p. s in amphibian muscles in normal Ringer's solution, is discussed in relation to acetylcholine release at the motor nerve endings (KATZ and MILEDI, 1967).

EFFECTS OF DIVALENT CATIONS ON THE SPONTANEOUS TRANSMITTER RELEASE AT THE AMPHIBIAN NEUROMUSCULAR JUNCTION IN THE PRESENCE OF ETHANOL