Corey D P, Dubinsky J M, Schwartz E A
J Physiol. 1984 Sep;354:557-75. doi: 10.1113/jphysiol.1984.sp015393.
Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the 'whole-cell, gigaseal' technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). 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 methanesulphonate as an anion), an inward current remained. It activated at approximately -40 mV, reached a maximum at approximately 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 approximately -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 two exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of two exponentials. Both 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, 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.
从蝾螈视网膜中分离出单个杆状内节。采用“全细胞、千兆封接”技术（哈米尔、马蒂、内尔、萨克曼和西格沃思，1981年）研究其钙电流。细胞质中的可溶性成分与移液管中的溶液进行交换。在连续灌注过程中可更换外部溶液。膜电压由电压钳控制。在用非渗透性离子（即作为阳离子的四乙铵以及作为阴离子的天冬氨酸或甲磺酸盐）取代除钙以外的渗透性离子后，仍存在内向电流。它在约-40 mV时激活，在约0 mV时达到最大值，并随着膜进一步去极化而减小。当用钡替代外部钙时，电流大小增加。当用钴替代钙时，电流被阻断。在实验的最初3分钟内，电流达到最大值一半时的电压从约-22 mV移至-31 mV。在实验的整个过程中，电流的最大幅度持续下降。去极化步骤后钙电流激活的时间进程可用两个指数之和来描述。较慢指数的时间常数与电压有关。复极化后的失活也可用两个指数之和来描述。失活的两个时间常数均与电压无关（在-30至0 mV之间），且比激活的较慢时间常数更快。当内部钙浓度用10 mM乙二醇双四乙酸（EGTA）缓冲时，在持续去极化的几秒钟内钙电流不会失活。当EGTA浓度降至0.1 mM时，在持续去极化的几秒钟内钙电流下降且膜电导降低。这种失活是不完全的，且仅在大量钙进入后才发生。复极化后钙电导从失活状态恢复。相比之下，在实验过程中观察到的持续下降（第3项）是不可逆的。这种差异表明失活和下降是不同的过程。
