Cytoplasmic Ca2+ release induced by microinjection of Ca2+ and effects of microinjected divalent cations on Ca2+ sequestration and exocytosis of cortical alveoli in the medaka egg.
Intracellular release of Ca2+ by microinjection of Ca2+ was analyzed by measuring the luminescence of aequorin loaded in eggs of the medaka (Oryzias latipes). Microinjection of Ca2+ into the cortical cytoplasm induced propagative waves of cytoplasmic Ca2+ release and exocytosis of cortical alveoli initiated at the injection point. The Ca2+ wave was initiated with a time lag after some was sequestered at the region of the microinjection. Microinjection of Mg2+ or Mn2+ failed to trigger Ca2+ release and exocytosis. When the aequorin-loaded eggs were inseminated after microinjection of Mg2+, Mn2+, or Co2+ into a restricted region of the vegetal hemisphere, the wave of Ca release was propagated through the injected region toward the vegetal pole, but neither Ca sequestration (fall in Ca-aequorin luminescence) nor exocytosis occurred at the area of cortex where the eggs were injected with these divalent cations. These results suggest that a significant period is required to induce Ca2+ release from cytoplasmic stores by the increased Ca2+ concentration and that both the phenomena of Ca2+ release and Ca sequestration are involved in the process of exocytosis.
Iwamatsu
T
T
Department of Biology, Aichi University of Education, Kariya, Japan.
Yoshimoto
Y
Y
Hiramoto
Y
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology*; D005089:Exocytosis / Q000187:drug effects*; D005399:Fishes / Q000378:metabolism; D007424:Intracellular Fluid / Q000032:analysis; D008274:Magnesium / Q000494:pharmacology*; D008345:Manganese / Q000494:pharmacology*; D008845:Microinjections; D010063:Ovum / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure
D003035:Cobalt; D008345:Manganese; D008274:Magnesium; D002118:Calcium