Effects of caffeine on neuromuscular transmission in the frog

Caffeine (10^-4 g./ml.) was used to attempt to alter intracellular Ca levels in frog motor nerve terminaIs; the effects of this treatment on standard parameters of transmitter release were studied. These effects included: an increase of 30% in the amplitude of the end-plate potential (e.p.p.), with most of the increase deriving from an increased amplitude of the miniature end-plate potential (m.e.p.p.); an increase of 80% in the resting m.e.p.p. frequency; a transient increase of 15%, followed by a sustained depression of 50%, in m.e.p.p. frequency in 15 mM K; a slowing of the rate of decline of post-tetanic potentiation of m.e.p.p. frequency; and a marked reduction in post-tetanic potentiation of e.p.p. amplitude. The significance of these results for the mechanism of transmitter release is discussed, with particular reference to the control of Ca activity in the immediate vicinity of the transmitter release sites