EFFECTS OF HG2+ AND CU2+ ON THE CYTOSOLIC CA2+ LEVEL IN MOLLUSCAN BLOOD-CELLS EVALUATED BY CONFOCAL MICROSCOPY AND SPECTROFLUOROMETRY

In the present work the effects of Hg2+ and CU2+ on the level of cytosolic Ca2+ in mussel (Mytilus edulis L.) haemolymph cells were investigated by confocal microscopy and spectrofluorimetry utilizing the fluorescent dye Fluo3. In the blood cells of marine molluscs, exposure to CU2+ and Hg2+ in the nanomolar and micromolar range causes a time- and concentration-dependent increase in the cytosolic Ca2+ level. Both the presence of a low-calcium containing medium and pretreatment of the cells with the channel blocker Verapamil greatly reduced the effects of higher (50 mu M) Hg2+ concentrations, this indicating that Hg2+ enhances the influx of extracellular Ca2+ partly through activation of voltage-dependent Ca2+ channels. Low concentrations of Hg2+ (1 mu M) and also of CU2+ (0.5 mu M), an ''essential'' element, were able to induce a sustained increase in cytosolic Ca2+, which was not affected either by Verapamil pretreatment or by lowering the extracellular calcium concentration. These data indicate that in mussel haemocytes heavy metal cations impair Ca2+ homeostasis not only by affecting Ca2+ channels, but also by interfering with other mechanisms of calcium transport across cellular membranes, such as the Ca2+-ATPases. The resulting increase in cytosolic Ca2+ could activate Ca-dependent processes which may be involved in many of the biochemical and physiological alterations observed in the cells of metal-exposed mussels. Specimens used in these experiments were collected from the river Linker near Plymouth, U.K. in June 1991.