ABSTRACT
This study deals with the effects of chemical pollutants on the transmembrane potential difference for sodium 
in smooth muscle cells of Mytilus edulis. A method for indirect determination of extracellular space, intracellular ion concentrations and 
has been developed and is applied in the investigations. The determination is based on concentration data from haemolymph and muscle tissue samples. The precision of the method used was tested by direct measurements of the apparent intracellular concentration of sodium and the membrane potential. On the basis of these tests, the method was evaluated as reasonably good.
The method was used to study the sensitivity of the transmembrane 
in Mytilus edulis to 96 h exposures to various sublethal concentrations of formaldehyde, methanol and mercury. Both formaldehyde and mercury induced a depression of 
. The observed depressions could be ascribed to a change in both the electrogenic and the chemical components of 
. A depression of 
was associated with subsequent clinical injury and death. Methanol did not cause death or any changes in 
. Because of the observed correlation between depression of 
and clinical injury, 
is suggested to have a potential as an indicator of toxicity.
