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

The electrochemical potential difference of sodium (sodium gradient) a cross cell membranes is the energy source of a number of important cel lular functions, and failure to maintain the gradient is likely to aff ect these functions. The present investigation shows that the normal v alue of the gradient in the posterior adductor muscle of the blue muss el is about 10 000 J/mol, but a number of organic chemical compounds ( oil, oil dispersants, formaldehyde and benzene) cause the value to dro p. subsequently, these compounds also lead to death among the animals. The results show furthermore that the mussels tolerate a moderate red uction 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 valu e of about 6000 J/mol, the reversibility of the gradient depression se ems 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 gradie nt is accompanied by a marked increase in the cellular content of calc ium, which may be the direct cause of cellular death. The transmembran e sodium gradient and the cellular calcium content may have an interes ting application as parameters for ecologically relevant evaluation of the toxicity of environmental pollutants.