PMID: 8951080Nov 1, 1996Paper

Extracellular Ca2+ entry and Ca2+ release from inositol 1,4,5-trisphosphate-sensitive stores function at fertilization in oocytes of the marine bivalve Mytilus edulis

Development
R DeguchiM Morisawa

Abstract

An oocyte of the marine bivalve Mytilus edulis, which is arrested at metaphase I, reinitiates meiosis at fertilization. The fertilized oocyte shows increases in intracellular Ca2+ ([Ca2+]i) comprising three different phases: an initial large [Ca2+]i transient, a subsequent low but sustained [Ca2+]i elevation, and repetitive small [Ca2+]i transients. In this study, we have investigated the sources and mechanisms of the sperm-induced [Ca2+]i increases. Application of methoxyverapamil (D-600), an inhibitor of voltage-dependent Ca2+ influx, suppressed the initial [Ca2+]i transient but did not affect the following two phases of [Ca2+]i changes. Injection of heparin, an antagonist of the inositol 1,4,5-trisphosphate (IP3) receptor, inhibited the later two phases without much affecting the initial transient. Combined application of D-600 and heparin almost completely abolished the three phases of the sperm-induced [Ca2+]i changes. Furthermore, Ca2+ influx caused by seawater containing excess K+ was blocked by D-600 but not by heparin, and IP3-induced Ca2+ release caused by photolysis of injected 'caged' derivatives of IP3 was blocked by heparin but not by D-600. These results strongly suggest that two types of Ca2+ mobilization system...Continue Reading

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