An in vitro study of copper and copper chelators on the crayfish stretch receptor

This study demonstrates the effects of micromolar concentrations of copper on the discharge firing activity of the isolated crayfish stretch receptor. Different pharmacological profiles of action were obtained with the divalent (cupric) and monovalent (cuprous) salt solutions. Cupric solutions produced a concentration-dependent triphasic effect (depression-excitation-depression); in contrast, a monophasic effect (depression) was produced by cuprous solutions. The effectiveness of copper chelators, in reversing these effects, were compared with normal physiological solution. Only the first phase of the effects of cupric were partially reversed with physiological solution or ethylenediamine tetraammonium (EDTA). In the presence of D-penicillamine and triethylene tetramine (trien), all phases of the effects of both cuprous and cupric salts were completely restored to control values. In addition, copper was shown to be the most neurotoxic divalent cation examined. The results demonstrate that effects of copper on neuronal activity are dependent on time, concentration and valency state.