Voltage-clamp study of the conductance activated at fertilization in the starfish egg.
Voltage-clamp study of the conductance activated at fertilization in the starfish egg.
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海星卵受精时激活的电导的电压钳研究。
DOI：
10.1113/jphysiol.1983.sp014982
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
Lansman,JB
中科院分区：
文献类型：
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作者：
Lansman,JB
利用双微电极电压钳研究了海星卵受精潜力的离子电流。成熟卵子在电压箝位条件下体外受精。受精流，这里称为IF，是通过将精子加入浸泡在卵子中的海水中来诱导的。在‐70 mV的保持电位下，中频向内。它在2 - 4分钟内达到峰值，然后在接下来的大约20分钟内衰减，其速率取决于保持膜电位。在中频过程中不同时间测量的瞬时电流-电压关系近似为线性，在+6.0 +/‐5.8 mV的电位下（平均+/‐sd， n = 11）反向。膜弦电导在向内电流峰值时最高，而IF的下降阶段是由于电导向受精前水平下降所致。当膜电位迅速上升到高于- 45 mV的水平时，中频电导的下降取决于膜电位和时间。受精特异电导在- 50 ~ +10 mV之间呈s型激活曲线，半激活水平为- 25 mV。稳态电压依赖性分析表明，在施肥势的峰值（+10 ~ +15 mV），只有4% - 5%的可用通道是开放的。电流弛豫遵循一阶动力学，弛豫时间常数取决于电压脉冲期间的膜电位。时间常数与电压呈钟形关系，在负电位大于- 40和正电位大于0 mV时减小。稳态电导-电压关系和电流弛豫动力学都与简单的两态门控模型一致，其中通道打开的概率由单个有效价为‐1.7的门控粒子通过整个膜场决定。利用恒场表达式分析了反转电位随外部Na（在10 mM‐外部K）变化的变化，该表达式给出了Na对K的相对渗透率约为0.6。（摘要删节为400字）
Ionic currents underlying the fertilization potential of the egg of the starfish Mediaster aequalis were studied using a two‐micro‐electrode voltage clamp. Mature eggs were fertilized in vitro under voltage‐clamp conditions. The fertilization current, here termed IF, was induced by adding sperm to sea water bathing the egg. At a holding potential of ‐70 mV, IF was inward. It reached a peak within 2‐4 min and then decayed over the next approximately 20 min with a rate which depended on the holding membrane potential. Instantaneous current‐voltage relations measured at different times during IF were approximately linear and reversed at a potential of +6.0 +/‐ 5.8 mV (mean +/‐ S.D., n = 11). Membrane chord conductance was highest at the peak of inward current and the declining phase of IF was due to a decrease in conductance towards the pre‐fertilization level. When the membrane potential was rapidly stepped to levels more positive than about ‐45 mV, the conductance underlying IF decreased in a manner which depended on both membrane potential and time. The fertilization‐specific conductance showed a sigmoidal activation curve between ‐50 and +10 mV with a half‐activation level of ‐25 mV. Analysis of the steady‐state voltage dependence indicated that at the peak of the fertilization potential (+10 to +15 mV) only 4‐5% of the total available channels would be open. Current relaxations followed first‐order kinetics and the relaxation time constant depended upon the membrane potential during the voltage pulse. The relation between the time constant and voltage was bell‐shaped, decreasing at potentials more negative than ‐40 and more positive than 0 mV. Both the steady‐state conductance‐voltage relation and the kinetics of the current relaxations were consistent with a simple two‐state gating model in which the probability of a channel being open is determined by a single gating particle with an effective valency of ‐1.7 moving through the entire membrane field. The shifts in reversal potential with changes in external Na (at 10 mM‐external K) were analysed using the constant field expression, which gave a relative permeability of Na to K of approximately 0.6.(ABSTRACT TRUNCATED AT 400 WORDS)