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).

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 Ca , inositol, 1, 4, 5-trisphosphate (IP ), Ca-ionophore A23187, cGMP, GMP, GTP and guanosine 5'-0-(2-thio-triphosphate)(GTP-γ-s), while CAMP, ATP, gnanosine 5'-0-(2-thio-triphosphate)(GDP- β-s), inositol monophosphate (IMP) and inositol triphosphate (ITP) were ineffective. Ca , IP and A231 87 induced the propagative exocytosis after a time lag (5-8 sec), irrespective of the presence of Co . The time lag was shorter than that (13-28 sec) following microinjection of cGMP or GTP, while were not effective in the presence of Co . The present data suggest that (1) free cytoplasmic Ca participates in both an early and a late step in exocytosis, and (2) cGMP or GTP acts on an early step before initiation of Ca release during exocytosis in the medaka egg.