Goudeau M, Goudeau H
Laboratoire de Biologie et Physiologie Cellulaires Marines, Université de Nice-Sophia Antipolis, France.
Dev Biol. 1993 Nov;160(1):165-77. doi: 10.1006/dbio.1993.1295.
The fertilization potential of the Phallusia mammillata egg has been found to consist, in natural or standard artificial sea water (NSW and ASW), of an initial sperm-triggered rapid depolarization comprising two distinct successive components, followed by a phase of membrane depolarization comprising a plateau and two series of membrane potential oscillations. These oscillations occur during meiotic divisions and they end just before formation of the second polar body. In the present work, the effects of removing external Ca2+ on the fertilization potential time course on the rate of polyspermy and on the resumption of meiosis of the P. mammillata egg were explored. Eggs inseminated in Ca(2+)-free ASW usually responded by several successive sperm-induced electrical responses strikingly different from that obtained in standard ASW: removing external Ca2+ during insemination and the initial depolarizing shift (free (Ca2+), 5-11 microM in Ca(2+)-free ASW) and during the subsequent period of the electrical responses (free (Ca2+), 0.2 microM in Ca(2+)-free ASW), completely suppressed both the second component of the initial depolarizing shift, the plateau, and membrane oscillations of the depolarization phase, did not impair sperm entry, but always blocked the resumption of meiosis. Under these conditions eggs were polyspermic (91%, n = 22, c.l. 69-99%). Lastly, only a short period of contact (approximately 20 sec at minimum) with a physiological concentration of external Ca2+ (12 mM) at the onset of the fertilization potential was necessary for the egg to resume meiosis and then to undergo complete embryonic development. These results indicate that in the P. mammillata egg, the second component of the initial depolarizing shift involves voltage-gated Ca2+ channels. The possibility is discussed that external Ca2+ ions might contribute to the activation of the P. mammillata egg by providing a source for an increase of (Ca2+)i and/or for the reloading of the Ca2+ internal stores.
已发现海鞘卵在天然或标准人工海水中（NSW和ASW）的受精电位由最初精子引发的快速去极化组成，该去极化包括两个不同的连续成分，随后是膜去极化阶段，包括一个平台期和一系列膜电位振荡。这些振荡发生在减数分裂期间，并在第二极体形成之前结束。在本研究中，探讨了去除外部Ca2+对海鞘卵受精电位时间进程、多精入卵率和减数分裂恢复的影响。在无Ca2+的ASW中受精的卵通常会产生几次连续的精子诱导电反应，这与在标准ASW中获得的反应明显不同：在受精期间和初始去极化转变期间（无Ca2+的ASW中游离Ca2+为5-11 microM）以及随后的电反应期间（无Ca2+的ASW中游离Ca2+为0.2 microM）去除外部Ca2+，完全抑制了初始去极化转变的第二个成分、平台期以及去极化阶段的膜振荡，不影响精子进入，但总是阻止减数分裂的恢复。在这些条件下，卵是多精入卵的（91%，n = 22，置信区间69-99%）。最后，在受精电位开始时，卵只需与生理浓度的外部Ca2+（12 mM）短时间接触（至少约20秒），就可以恢复减数分裂，然后进行完整的胚胎发育。这些结果表明，在海鞘卵中，初始去极化转变的第二个成分涉及电压门控Ca2+通道。讨论了外部Ca2+离子可能通过为细胞内Ca2+增加提供来源和/或为Ca2+内部储存重新加载来促进海鞘卵激活的可能性。
