The inhibitory effect of cadmium on neuromuscular transmission in the rat

Cadmium (0.125-1 mM) was found to inhibit the isometric response of the isolated rat hemidiaphragm during indirect stimulation, but not during direct stimulation. This effect of cadmium (1 mM) was completely reversed by ethyleneglycol bis-(aminoethyl)-N,N,N',N'-tetra-acetic acid (2 mM) or by L-cysteine (2 mM) but only partially by increased calcium. Cadmium (10 micronM) significantly reduced the quantal release of transmitter in the isolated phrenic diaphragm and a concentration of 0.1 mM frequently caused a complete failure of the endplate response after 30 min. The effect of cadmium on neuromuscular transmission could not be readily reversed by washing with cadmium-free solution. Miniature endplate potential frequency and amplitude were not significantly affected by cadmium (0.1 or 0.5 mM). The results suggest that the effect of cadmium on the isolated phrenic nerve-diaphragm is due largely to inhibition of calcium function at presynaptic nerve terminals.