Mercury chloride induces changes in the Mg2+-stimulated membrane currents in oocytes of the prawn Palaemon serratus

In the prawn Palaemon serratus, seawater Mg2+ ions trigger oocyte activation events in the absence of spermatozoon. The effect of mercury chloride on the conductance of unactivated prawn oocytes and the functioning of K-Ca(+) and Na-Ca(+) channels sequentially involved in the electrical response of prawn oocytes stimulated with external Mg2+ was examined. In unactivated oocytes, 20 mu M Hg2+ induced a significant increase in membrane conductance after 15 min of incubation. Moreover, micromolar amounts of Hg2+ ions (1-20 mu M) affected, in both a dose- and voltage-dependent manner, the functioning of Ca2+-dependent K+ channels implicated in the first phase of the Mg2+-induced electrical response of prawn oocytes. Treatment of oocytes with 5 and 10 mu M Hg2+ ions significantly diminished the maximal value of this initial Mg2+-triggered outward K+ current, while 20 mu M Hg2+ completely inhibited this response after 20 min of incubation. Maximal treatments of 10 and 20 mu M Hg2+ greatly increased the inward current involved in the second phase of the Mg2+-induced electrical response of prawn oocytes, consequently inducing an increase in membrane conductance. This final increase in conductance elicited by Hg2+ ions reflects a change in the selectivity of Ca2+-dependent Na+ channels. (C) 1999 Elsevier Science B.V. All rights reserved.