ACTION OF VERAPAMIL ON THE RATE OF SPONTANEOUS RELEASE OF TRANSMITTER AT THE FROG NEUROMUSCULAR-JUNCTION

Verapamil is known to reduce Ca2+ entry in a variety of cells. At 10-5 M it produces a small reduction in MEPP frequency at the frog neuromuscular junction, whereas the rate of spontaneous release rises following treatment at a concentration of 10-4 M. This latter effect is augmented by raising [Ca2+]0 to 9 mM or, more especially, by raising the temperature from 17 to 23°C. It is argued that both these opposing effects are related to the action of verapamil in modiying [Ca2+]i at the presynaptic terminals and its is suggested that the drug can affect both inward Ca2+ flux (so reducing the steady-state position of [Ca2+]i) and also, at higher concentration, either inhibit the membrane Ca2+ pump or cause the release of Ca2+ from intracellular Ca2+ stores (so raising [Ca2+]i). © 1979.