Effects of heavy metals on phospholipase C in gill and digestive gland of the marine mussel Mytilus galloprovincialis Lam

We studied the in vivo and in vitro effects of Hg²⁺ and Cu²⁺ on the activity of phospholipase C (PLC), specific for phosphatidylinositol 4,5-bisphosphate, in the mussel (Mytilus galloprovincialis Lam). The enzyme activity was assayed in tissue homogenates from gills and digestive gland. The toxic effect of Hg²⁺ appeared to be stronger than that of Cu²⁺ both in vitro and in vivo, especially for the digestive gland. In in vitro tests, Hg²⁺ was able to inhibit PLC activity when added directly to the reaction mixture. Conversely, Cu²⁺ was effective only after preincubation, suggesting that the effect of the metal may be derived from lipid peroxidation due to Cu²⁺-induced oxyradical production. Treatment of mussels with sublethal concentrations of Hg²⁺ or Cu²⁺ in vivo produced significant PLC inhibition after 1 or 4 days, respectively. A recovery was reached after 7 days of in vivo metal incubation. Data indicate that in mussel gills and digestive gland heavy metals impair PLC activity, thereby affecting IP₃-dependent Ca²⁺ signaling. (C) 2000 Elsevier Science Inc.