Activation of Sea Urchin Eggs by Halothane and Its Inhibition by Dantrolene

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Abstract
Eggs of the sea urchin, Hemicentrotus pulcherrimus, were stimulated by halothane, known to induce Ca2+ release from sarcosome, to cause fertilization membrane formation in normal and Ca2+ free artificial sea water. In the absence of external Ca2+, halothane-induced formation of fertilization membrane was inhibited by dantrolene, an inhibitor of Ca2+ release from sarcosome, but was not blocked by nifedipine, a Ca2+ antagonist specific to Ca2+ channels in plasma membrane. Ca2+ release from sedimentable fraction isolated from eggs was induced by halothane and was inhibited by dantrolene, but was not blocked by nifedipine. In normal artificial sea water, halothane-caused egg activation was not inhibited either by dantrolene or by nifedipine, but was blocked in the presence of both compounds. 45Ca2+ influx was substantially stimulated by halothane in eggs exposed to 45CaCl2. Halothane-induced 45Ca2+ influx into eggs was inhibited by nifedipine but was not blocked by dantrolene. When Ca2+ release from intracellular organellae is blocked, Ca2+ transport through Ca2+ channels in plasma membrane probably acts as a "fail-safe" system to induce an increase in cytosolic Ca2+ level, resulting in egg activation.