Inhibitory effects of cadmium on the release of acetylcholine from cardiac nerve terminals

The effect of stimulation of the vagaosympathetic trunk or the vagal nerve on the cardiac interval of the spontaneously beating heart of the bullfrog was studied in the presence and absence of Cd. The prolongation of the cardiac interval following the nerve stimulation was abolished by Cd (5 micrometer). Such an effect of Cd was completely antagonized by increasing the external Ca to 10 times the normal concentration. Cd (10 micrometer) 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 the effluent from the heart after cardiac nerve stimulation showed that Cd reduced the acetylcholine release from the cardiac nerve. It is concluded that Cd may act on the cardiac nerve terminals where Cd suppresses the release of acetycholine.