Correlation of calpain activity level and some membrane lipid component contents in organs of mussels, Mytilus edulis L., was shown in aquarial experiment on the study of mussel response reactions on the exposure of different levels of copper and cadmium. The correlation observed possibly could be explained by the effector role of membrane lipid components (arachidonic acid, phosphatidylinositol) on Ca(2+)-channels. Thus, the correlation between tissue lipid composition and protein functional activity was demonstrated with intracellular Ca2+ level as a key member.