Effects of KCl-EGTA solution on the isolated Mytilus smooth muscle: a method for denervation

The ABRM of M. edulis was immersed in KCl-EGTA solution (540 mM KCl + 5 mM EGTA) for 30 min. Then the muscle was returned to normal ASW, effects of the KCl-EGTA solution being examined on the ultrastructure of the neuromuscular junctions and also on the mechanical responses of the muscle to several kinds of stimuli. By the KCl-EGTA treatment of the muscle, synaptic vesicles in the nerve terminals at the junctions were found to be markedly deformed in shape and materially reduced in number. In most of the muscles tested, the contractile response to ACh and catch-relaxing responses to serotonin and dopamine were not depressed by the present treatment, though in some other muscles those responses were depressed a little. Contractile and catch-relaxing responses to repetitive electrical pulses of stimulation were markedly depressed or almost blocked by the treatment. All of the catch-relaxing responses to hexylamine (10(-3)M), phenylethylamine (10(-4)M), Na+-free ASW and 8-bromo-cyclic GMP (10(-3)M) were also markedly depressed or almost completely blocked. These results indicate that the function of intramuscular nerve fibres in the ABRM is markedly impaired by treating the muscle with KCl-EGTA solution while that of muscle fibres is little impaired. The treatment seems to be a useful method for denervation in the isolated ABRM.