title: 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.
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 systems, the extracellular Ca2+ entry responsible for an initial [Ca2+]i transient and the IP3 receptor-mediated Ca2+ release responsible for the following two phases of [Ca2+]i changes, function at fertilization of Mytilus oocytes.
authors.affiliation: Misaki Marine Biological Station, University of Tokyo, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Deguchi
authors.forename: K
authors.initials: K
authors.lastname: Osanai
authors.forename: M
authors.initials: M
authors.lastname: Morisawa
mesh_terms: D000818:Animals; D049872:Bivalvia / Q000196:embryology*; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002451:Cell Compartmentation; D005110:Extracellular Space / Q000502:physiology; D005306:Fertilization; D005711:Gallopamil / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008540:Meiosis; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D015398:Signal Transduction
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D005711:Gallopamil; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D011188:Potassium; D002118:Calcium