A POSSIBLE ROLE OF INTRACELLULAR Ca²⁺ IN THE REGULATION OF THE ACh RECEPTOR-ION CHANNEL COMPLEX OF THE SYMPATHETIC GANGLION CELL

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Effects of caffeine (2-6 mM) on the nicotinic transmission of the bullfrog sympathetic ganglion was studied by using an intracellular recording technique. Caffeine (2-4 mM) decreased the amplitude, quantal content and quantal size of the fast e. p. s. p. and the amplitude of ACh potential. Under these conditions, resting membrane potential was almost unchanged with a slight decrease in the membrane resistance. Injection of “EGTA” increased the amplitude of the fast e. p. s. p. under the effect of caffeine (6 mM). These results suggest that caffeine suppresses the nicotinic transmission of the bullfrog sympathetic ganglion by both the pre- and postsynaptic actions and that a considerable portion of the postsynaptic action was the result of a rise in the intracellular free Ca²⁺ concentration.