Exocytosis of Cortical Alveoli and Its Initiation Time in Medaka Eggs Induced by Microinjection of Various Agents. (cortical alveolus exocytosis/inositol 1, 4, 5-trisphosphate/microinjection/medaka egg)

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Abstract
Various agents were microinjected into the cortical cytoplasm at the animal pole of unfertilized eggs of Oryzias latipes under Ca-free conditions. The agents that triggered a wave of the cortical alveolus exocytosis were Ca2+, inositol 1,4,5-trisphosphate (IP3), Ca-ionophore A23187, cGMP, GMP, GTP and guanosine 5''-0-(2-thio-triphosphate) (GTP-.gamma.-s), while cAMP, ATP, guanosine 5''-0-(2-thio-triphosphate)(GDP-.beta.-s), inositol monophosphate (IMP) and inositol triphosphate (ITP) were ineffective. Ca2+, IP3 and A23187 induced the propagative exocytosis after a time lag (5-8 sec), irrespective of the presence of Ca2+. The time lag was shorter than that (13-28 sec) following microinjection of cGMP or GTP, while were not effective in the presence of Ca2+. The present data suggest that (1) free cytoplasmic Ca2+ participates in both an early and a late step in exocytosis, and (2) cGMP or GTP acts on the early step before initiation of Ca2+ release during exocytosis in the medaka egg.