Arnoult C, Grunwald D, Villaz M
Laboratoire de Biophysique Mol'eculaire et Cellulaire, CNRS URA 520, Grenoble, France.
Dev Biol. 1996 Mar 15;174(2):322-34. doi: 10.1006/dbio.1996.0077.
The conductance change after fertilization in the oocyte of the ascidian Ciona intestinalis has been followed by the whole cell patch-clamp technique. Two new inward currents, which are absent in unfertilized eggs, are elicited by hyperpolarization from a holding potential of +20 mV, which is the resting potential soon after fertilization. These currents reach their maximum level during the first meiotic division cycle, and then decrease in intensity, becoming almost undetectable at the 2-cell stage. These currents are most easily seen at high concentrations of barium. At least one, and likely both, of these currents appears to be carried by Ca ions. One of the currents is blocked by low concentrations of gadolinium; the other one is blocked by higher concentrations, although gadolinium at these levels does not block fertilization and the associated early depolarizing jump of the eggs. Thus these currents are not carried by channels that mediate the fertilization current. However, gadolinium blocks normal transition to 2-cell stage and blocks current oscillations synchronous to free calcium oscillations that occur normally in eggs around meiosis II. The electrical signature of calcium-release activated currents, taken together with these findings, suggests that these inward currents ensure a calcium entry pathway throughout meiosis. A plausible function of these currents may be to refill the Ca stores that are depleted after fertilization and that are required to progress into mitotic cell division. This interpretation is reinforced by experiments on unfertilized eggs with intracellular Ca stores depleted by thapsigargin, where both the newly described currents are observed.
利用全细胞膜片钳技术跟踪了海鞘Ciona intestinalis卵母细胞受精后的电导变化。从 +20 mV的钳制电位进行超极化可引出两种新的内向电流，未受精卵中不存在这两种电流，而 +20 mV是受精后不久的静息电位。这些电流在第一次减数分裂周期达到最大水平，然后强度下降，在2细胞期几乎检测不到。在高浓度钡的情况下最容易观察到这些电流。这些电流中至少有一种，可能两种，似乎都是由钙离子携带的。其中一种电流被低浓度的钆阻断；另一种被较高浓度的钆阻断，不过在这些浓度下钆不会阻断受精以及卵子相关的早期去极化跃变。因此，这些电流不是由介导受精电流的通道携带的。然而，钆会阻断向2细胞期的正常转变，并阻断与减数分裂II期前后卵子中正常发生的游离钙振荡同步的电流振荡。结合这些发现，钙释放激活电流的电信号表明，这些内向电流确保了整个减数分裂过程中的钙进入途径。这些电流的一个合理功能可能是补充受精后耗尽的钙库，而这些钙库是进入有丝分裂细胞分裂所必需的。用毒胡萝卜素耗尽细胞内钙库的未受精卵实验强化了这一解释，在这些未受精卵中观察到了新描述的两种电流。
