Hg(2+) affects the intracellular free Ca(2+) oscillatory pattern and the correlated membrane conductance changes in Mg(2+)-stimulated oocytes of the prawn Palaemon serratus.
The impact of mercuric ions (Hg(2+)) on prawn oocytes was examined. Prawn oocytes constitute an unusual system in that they are activated at spawning by seawater Mg(2+), which mediates correlated dynamic changes in intracellular free calcium concentration [(Ca(2+))(i)] and membrane conductance associated with the meiosis resumption. Using a voltage clamp technique and intracellular calcium measurements, we observed that treatment with Hg(2+) (5, 10, and 20 microM) resulted in simultaneous impairments of both (Ca(2+))(i) and membrane current responses to external Mg(2+). Treatment with Hg(2+) also resulted in a gradual dose-dependent slow increase in the baseline level of both (Ca(2+))(i) and membrane conductance, independent of stimulation with external Mg(2+). The effect of Hg(2+) on (Ca(2+))(i) and membrane conductance changes resulted from a block of the signal transduction pathway at some point before the InsP(3) receptor channel involved in Ca(2+) release from the endoplasmic reticulum (ER) stocks. The Hg(2+)-dependent gradual increase in both (Ca(2+))(i) and membrane conductance baseline levels may potentially result from a slow permeabilization of the ER membrane, resulting in Ca(2+) leaking into the cytosol. Indeed, this effect could be blocked with the cell permeable Hg(2+) competitor dithiothreitol, which was able to displace Hg(2+) from its intracellular target regardless of whether external Ca(2+) was present or not.
Observatoire Océanographique et de Biologie marine, CNRS and Université Pierre et Marie Curie, Station biologique de Roscoff, 29682 Roscoss, cedex, France.
Marie
M
Goudeau
Henri
H
Goudeau
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects; D004229:Dithiothreitol / Q000494:pharmacology; D004553:Electric Conductivity; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008274:Magnesium / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008540:Meiosis / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects*; D008628:Mercury / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D033541:Palaemonidae / Q000166:cytology*; D010539:Permeability / Q000187:drug effects; D012623:Seawater; D015398:Signal Transduction / Q000187:drug effects
D007473:Ion Channels; D008628:Mercury; D008274:Magnesium; D002118:Calcium; D004229:Dithiothreitol