IN-VIVO EFFECTS OF COPPER ON THE CALCIUM HOMEOSTASIS MECHANISMS OF MUSSEL GILL CELL PLASMA-MEMBRANES

In vivo effects of Cu2+ on the Ca2+ homeostasis mechanisms of gill cel l plasma membranes were assessed in mussels (Mytilus galloprovincialis ) exposed for 1, 4, and 7 days to sublethal concentrations of Cu2+ (0. 6 mu M), by quantifying the activity of Ca2+ ATPase and Na+/K+ ATPase on a plasma membrane-enriched subcellular fraction. Enzyme activities showed an initial decrease reaching a minimum after four days of metal exposure (about 60-70 % inhibition), followed by a recovery. Impairme nt of the Ca2+-ATPase activity was due to an inhibition of the phospho rylated intermediate formation. The inhibition of the plasma membrane Ca2+-ATPase activity is a direct evidence of metal effects on Ca2+ hom eostasis processes, while the inhibition of the Na+/K+ ATPase could al so involve an impairment of the Na+/Ca2+ antiporter. Copper-induced en zyme deterioration probably derives from the high affinity oi the meta l for SH groups, but a role could also be played by metal-induced oxid ative stress and consequent lipid peroxidation of cell membranes, as s uggested by glutathione depletion and MDA increase, respectively. Reco very of enzyme functionality and glutathione levels, notwithstanding p rogressive Cu2+ accumulation in mussel gill tissue, suggests the activ ation of metal induced cell detoxification systems.