Serotonin-induced meiosis reinitiation from the first prophase and from the first metaphase in oocytes of the marine bivalve Hiatella flaccida: respective changes in intracellular Ca2+ and pH.
In the marine bivalve Hiatella flaccida, full-grown oocytes in ovaries are arrested at the first prophase (prophase-I) of meiosis, whereas spawned oocytes have reinitiated meiosis from prophase-I and are again arrested at the first metaphase (metaphase-I). The neurohormone serotonin (5-hydroxytryptamine, 5-HT) was able to trigger meiosis reinitiation both from prophase-I and from metaphase-I. Exposure of prophase-I oocytes to 5-HT caused an increase in intracellular Ca2+ ([Ca2+]i) composed of an initial towering transient and a following lower but sustained elevation. 5-HT-stimulated prophase-I oocytes also showed a gradual rise in intracellular pH (pHi), reaching a plateau level. None of these 5-HT-induced responses was affected by the complete absence of external Ca2+. On the other hand, these responses were suppressed by preinjection of heparin, an antagonist of inositol 1,4,5-trisphosphate-sensitive receptors. Metaphase-I oocytes also exhibited a [Ca2+]i increase in response to 5-HT; the initial [Ca2+]i transient was larger than that in prophase-I oocytes when stimulated with the same 5-HT concentration. Furthermore, after the initial transient, the elevated [Ca2+]i was not sustained but sometimes returned to the prestimulus level and then increased again. Metaphase-I oocytes had higher resting pHi levels than prophase-I oocytes and showed no significant pHi changes after addition of 5-HT. These results suggest that both a [Ca2+]i increase and a pHi rise are responsible for the release from prophase-I arrest, while a [Ca2+]i increase alone is concerned with the release from metaphase-I arrest.
Deguchi
R
R
Asamushi Marine Biological Station, Tohoku University, Aomori, Japan.
Osanai
K
K
D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D008540:Meiosis / Q000187:drug effects*; D008677:Metaphase; D008974:Mollusca; D009865:Oocytes / Q000378:metabolism*; D011418:Prophase; D012701:Serotonin / Q000494:pharmacology*
D012701:Serotonin; D015759:Ionomycin; D000641:Ammonia; D006493:Heparin; D002118:Calcium