Hg2+ affects the intracellular free Ca2+ oscillatory pattern and the correlated membrane conductance changes in Mg2+‐stimulated oocytes of the prawn Palaemon serratus

AbstractThe impact of mercuric ions (Hg2+) on prawn oocytes was examined. Prawn oocytes constitute an unusual system in that they are activated at spawning by seawater Mg2+, which mediates correlated dynamic changes in intracellular free calcium concentration [(Ca2+)i] and membrane conductance associated with the meiosis resumption. Using a voltage clamp technique and intracellular calcium measurements, we observed that treatment with Hg2+ (5, 10, and 20 μM) resulted in simultaneous impairments of both (Ca2+)i and membrane current responses to external Mg2+. Treatment with Hg2+ also resulted in a gradual dose‐dependent slow increase in the baseline level of both (Ca2+)i and membrane conductance, independent of stimulation with external Mg2+. The effect of Hg2+ on (Ca2+)i and membrane conductance changes resulted from a block of the signal transduction pathway at some point before the InsP3 receptor channel involved in Ca2+ release from the endoplasmic reticulum (ER) stocks. The Hg2+‐dependent gradual increase in both (Ca2+)i and membrane conductance baseline levels may potentially result from a slow permeabi‐lization of the ER membrane, resulting in Ca2+ leaking into the cytosol. Indeed, this effect could be blocked with the cell permeable Hg2+ competitor dithiothreitol, which was able to displace Hg2+ from its intracellular target regardless of whether external Ca2+ was present or not. © 2002 Wiley‐Liss, Inc.