Transmembrane sodium energy gradient and calcium content in the adductor muscle of Mytilus edulis L. in relation to the toxicity of oil and organic chemicals

Abstract

The electrochemical potential difference of sodium (sodium gradient) across cell membranes is the energy source of a number of important cellular functions, and failure to maintain the gradient is likely to affect these functions. The present investigation shows that the normal value of the gradient in the posterior adductor muscle of the blue mussel is about 10 000 J/mol, but a number of organic chemical compounds (oil, oil dispersants, formaldehyde and benzene) cause the value to drop. Subsequently, these compounds also lead to death among the animals. The results show furthermore that the mussels tolerate a moderate reduction of the sodium gradient, and that after moderate reductions the gradient returns to its normal value when the animals are transferred to clean sea water. However, if the sodium gradient drops below a value of about 6000 J/mol, the reversibility of the gradient depression seems to be lost, in that the sodium gradient in this case continues to fall even when the animals are transferred to clean seawater. In this situation the animals are moribund. The reduction in the sodium gradient is accompanied by a marked increase in the cellular content of calcium, which may be the direct cause of cellular death. The transmembrane sodium gradient and the cellular calcium content may have an interesting application as parameters for ecologically relevant evaluation of the toxicity of environmental pollutants.