Inositol trisphosphate-induced calcium release in the generation of calcium oscillations in bovine eggs.
Bovine eggs exhibit repetitive rises in intracellular calcium concentration ([Ca2+]i) in response to fertilization. The signaling pathways and Ca2 release mechanisms involved in their generation are not well characterized. This study examined the presence of a GTP-binding protein (G-protein) signaling pathway as well as the role of inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R)-mediated Ca2+ release and ryanodine receptor (RyR)-mediated Ca2+ release, the two Ca2+ receptors/channels most often thought to participate in the generation of [Ca2+]i oscillations, by injecting appropriate agonists and antagonists and monitoring their effects on Ca2+ release and pronucleus formation, injection of guanosine 5'-0-(3-thiotriphosphate) (GTP gamma [S]), which promotes G-protein-mediated phosphoinositide turnover, induced, at high concentrations, repetitive [Ca2+]i rises. Low concentrations of GTP gamma [S] were ineffective. Injection of inositol trisphosphorothioate (InsP3S3), a nonmetabolizable analogue of InsP3, evoked an immediate Ca2+ release followed by [Ca2R]i oscillations. The GTP gamma [S]- and InsP3S3-induced oscillations showed a rapid attenuation in amplitude and were terminated in about 30-60 min. Thimerosal, a thiol oxidizing agent, caused repetitive rises in [Ca2+]i by sensitizing Ca2+ injection-induced Ca2+ release. Injection of ryanodine, which stimulates Ca(2+)-induced Ca2+ release via the RyR, did not induce [Ca2+]i oscillations; and eggs into which it was preinjected exhibited normal [Ca2+]i oscillations in response to thimerosal. Preinjection of heparin, a competitive InsP3R antagonist, blocked in a dose-dependent manner the Ca2+ response to InsP3 and thimerosal, and its injection into fertilized oscillating eggs inhibited [Ca2+]i oscillations in all eggs.(ABSTRACT TRUNCATED AT 250 WORDS)
Fissore
R A
RA
Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst 01003, USA.
Pinto-Correia
C
C
Robl
J M
JM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D005260:Female; D005307:Fertilization in Vitro; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D013849:Thimerosal / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
D016877:Oxidants; D010716:Phosphatidylinositols; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D012433:Ryanodine; D013849:Thimerosal; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D019204:GTP-Binding Proteins; D002118:Calcium