Inhibitory Effects of Cadmium on the Release of Acetylcholine from Cardiac Nerve Terminals

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Abstract
The effect of stimulation of the vagaosympathetic trunk or the vagal nerve on the cardiac interval of the spontaneously beating heart of the bullfrog [Rana catesbeiana] was studied in the presence and absence of Cd2+. The prolongation of the cardiac interval following the nerve stimulation was abolished by Cd2+ (5 .mu.M). Such an effect of Cd2+ was completely antagonized by increasing the external Ca2+ to 10 times the normal concentration. Cd2+ (10 .mu.M) did not alter the compound action potential of the nerve trunk, nor did it affect the pacemaker activity of the heart. Bioassay of acetylcholine in th effluent from the heart after cardiac nerve stimulation showed that Cd2+ reduced the acetylcholine release from the cardiac nerve. Cd2+ may act on the cardiac nerve terminals where Ca2+ suppresses the release of acetycholine.