Change in intracellular Ca2+ is not involved in serotonin-induced meiosis reinitiation from the first prophase in oocytes of the marine bivalve Crassostrea gigas.
In response to the neurohormone serotonin (5-hydroxytryptamine, 5-HT), prophase-arrested oocytes of the marine bivalve Crassostrea gigas (oyster) reinitiate meiosis, undergo germinal vesicle breakdown (GVBD), and are arrested again at metaphase I. We examined the pharmacological characteristics of 5-HT receptors and the signal transduction pathway following 5-HT stimulation in oyster oocytes. Among 5-HT agonists tested, only alpha-methyl 5-HT, a 5-HT2 agonist, induced GVBD although it was 1000 times less sensitive than 5-HT. The rank order of the potency of 5-HT antagonists to inhibit GVBD was propranolol, cyproheptadine > metoclopramide > mianserin. These results are quite different from those reported for other mollusks, suggesting the presence of unique 5-HT receptors on oyster oocytes. Using the fluorescent Ca2+ dyes fura 2 and calcium green and the pH indicator 1-hydroxypyrene-3,6,8-trisulfonic acid, we examined changes in intracellular Ca2+ ([Ca2+]i) and intracellular pH (pHi) during 5-HT-induced meiosis reinitiation. 5-HT did not trigger any changes in [Ca2+]i. However, an increase in pHi was observed during the 5-HT-induced meiosis reinitiation. The increased pHi level was rather small before GVBD and not necessary for GVBD, because lowering pHi by sodium acetate seawater (pH 7.0) did not prevent 5-HT-induced GVBD. Measurement of the kinase activity toward a peptide substrate specific to cdc2 demonstrated that maturation-promoting factor (MPF) was activated in accordance with the occurrence of GVBD in response to 5-HT. Therefore, it is likely that in oyster oocytes the signal transduction pathways and intracellular effectors participating in 5-HT-induced meiosis reinitiation via the activation of MPF are insensitive to [Ca2+]i and pHi.
Kyozuka
K
K
Asamushi Marine Biological Station, Tohoku University, Aomori, Japan. kkyozuka@mail.cc.tohoku.ac.jp
Deguchi
R
R
Yoshida
N
N
Yamashita
M
M
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008540:Meiosis / Q000187:drug effects; D009842:Oligopeptides; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D010125:Ostreidae / Q000502:physiology*; D011418:Prophase; D011494:Protein Kinases / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D015398:Signal Transduction; D013379:Substrate Specificity
D009842:Oligopeptides; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D015544:Inositol 1,4,5-Trisphosphate; D011494:Protein Kinases; D002118:Calcium