THE CALCIUM CURRENT IN INNER SEGMENTS OF RODS FROM THE SALAMANDER (AMBYSTOMA-TIGRINUM) RETINA
THE CALCIUM CURRENT IN INNER SEGMENTS OF RODS FROM THE SALAMANDER (AMBYSTOMA-TIGRINUM) RETINA
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DOI：
10.1113/jphysiol.1984.sp015393
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发表时间：
1984-01-01
影响因子：
5.5
通讯作者：
SCHWARTZ, EA
中科院分区：
文献类型：
--
作者：
COREY, DP;DUBINSKY, JM;SCHWARTZ, EA
从蝾螈视网膜中分离出孤立的杆内节。用全细胞、千兆膜技术研究其钙电流。细胞质中的可溶性成分与移液管中的溶液交换。持续灌流过程中可改变外液。用电压钳控制膜电压。在用非渗透性离子（即，四乙基铵作为阳离子，天冬氨酸盐或甲磺酸盐作为阴离子），保持内向电流。它在. apprx激活。-40 mV，在0.0mV时达到最大值。0 mV，随着膜去极化程度的加深，其电位逐渐降低。当Ba替代外部Ca时，电流的大小增加。当用Co代替Ca时，电流被阻断。在实验的最初3分钟内，-22至-31 mV。在整个实验过程中，电流的最大振幅不断下降。去极化步骤后Ca电流激活的时间过程可用2个指数之和来描述。慢指数的时间常数与电压有关。复极化后的失活也可以用2个指数之和来描述。失活的时间常数与电压无关（在-30和0 mV之间），并且比活化的较慢时间常数快。当内部Ca浓度用10 mM-EGTA [乙二醇双[β-葡萄糖]缓冲时，氨基乙基醚]-N，N“-四乙酸]时，Ca电流在维持去极化的几秒钟内不增加。当EGTA的浓度降低到0.1 mM时，在维持去极化的几秒钟内，Ca电流下降，膜电导下降。这种失活是不完全的，仅在大量Ca进入后发生。复极化后，Ca电导从失活状态恢复。相反，在实验过程中观察到的连续下降（项目3）是不可逆的。这种差异表明，失活和下降是不同的过程。
Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the whole-cell, gigaseal technique. The soluble constituents of the cytoplasm exchanged with the solution in the pipette. The external solution could be changed during continuous perfusion. Membrane voltage was controlled with a voltage clamp. After permeant ions other than Ca were replaced with impermeant ions (i.e., tetraethylammonium as a cation, and aspartate or methanesulfonate as an anion), an inward current remained. It activated at .apprx. -40 mV, reached a maximum at .apprx. 0 mV, and decreased as the membrane was further depolarized. The size of the current increased when Ba was substituted for external Ca. The current was blocked when Ca was replaced with Co. The voltage at which the current was half-maximum shifted from .apprx. -22 to -31 mV during the initial 3 min of an experiment. The maximum amplitude of the current continuously declined during the entire course of an experiment. The time course for activation of the Ca current following a step of depolarization could be described by the sum of 2 exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of 2 exponentials. The time constants for deactivation were independent of voltage (between -30 and 0 mV) and faster than the slower time constant for activation. When the internal Ca concentration was buffered by 10 mM-EGTA [ethyleneglycol bis[.beta.-aminoethylether]-N,N''-tetraacetic acid], the Ca current did not inactivate during several seconds of maintained depolarization. When the concentration of EGTA was reduced to 0.1 mM, the Ca current declined and the membrane conductance decreased during several seconds of maintained depolarization. This inactivation was incomplete and only occurred after a substantial quantity of Ca entered. Following repolarization the Ca conductance recovered from inactivation. In contrast, the continuous decline observed during the course of an experiment (item 3) was not reversible. The difference suggests that inactivation and the decline are distinct processes.