Yatani A, Wilson D L, Brown A M
Cell Mol Neurobiol. 1983 Dec;3(4):381-95. doi: 10.1007/BF00734718.
Ca currents were examined with regard to their recovery from inactivation. The experiments were done on isolated nerve cell bodies of Helix aspersa using a combined suction pipet , microelectrode method for voltage clamp, and internal perfusion. Ca currents were separated by suppressing K and Na currents. The time course of recovery was determined by applying a test pulse at intervals ranging from 1 msec to 20 sec after prepulses varying from 20 to 3000 msec in duration. Each pair of pulses was preceded by a control pulse to ensure that the Ca currents had recovered before the next test pair was applied. Ba and Ca currents were compared and the effects of intracellular perfusion with EGTA, ATP, and vanadate were examined. Ba currents recovered in two stages and this time course was well fit by a sum of two exponentials with amplitudes and time constants given by A1 and tau 1 for the fast component and A2 and tau 2 for the slow component. In Ba the time constants were unchanged when prepulse durations were prolonged from 70 to 700 msec, although the initial amplitudes A1 and A2, particularly A2, were increased. Comparable influxes of Ca during the prepulse caused much more inactivation, but interestingly the recovery occurred at the same rate. The time course of Ca current recovery was also fit by a sum of two exponentials, the time constants of which were both smaller than the time constants of Ba current recovery. However, the time constants of Ca current recovery were increased markedly when prepulse durations were prolonged. Increasing the extracellular Ca concentration had a similar effect. Increasing the Ba influx had no effect on the recovery time constants, and the Ba results are consistent with reversible inactivation gating of potential-dependent membrane Ca channels. The Ca results show that Ca influx enhances inactivation. Intracellular perfusion with EGTA resulted in less inactivation in the cast of Ca but it had no effect on Ba currents. Intracellular ATP increased the rate of recovery of Ca currents, and intracellular vanadate inhibited recovery. It is concluded that recovery of Ca channels depends upon both Ca influx and membrane potential and is modulated by agents which affect Ca metabolism.
研究了钙电流从失活状态恢复的情况。实验采用联合吸引微吸管、电压钳微电极方法以及内部灌流技术，在分离的欧洲蜗牛神经细胞体上进行。通过抑制钾电流和钠电流来分离钙电流。恢复过程的时间进程是通过在持续时间为20至3000毫秒的预脉冲之后，每隔1毫秒至20秒施加一个测试脉冲来确定的。每对脉冲之前都有一个对照脉冲，以确保在下一对测试脉冲施加之前钙电流已经恢复。比较了钡电流和钙电流，并研究了用乙二醇双四乙酸（EGTA）、三磷酸腺苷（ATP）和钒酸盐进行细胞内灌流的影响。钡电流分两个阶段恢复，其时间进程可以很好地用两个指数之和来拟合，快速成分的幅度和时间常数分别为A1和τ1，慢速成分的幅度和时间常数分别为A2和τ2。在钡电流中，当预脉冲持续时间从70毫秒延长到700毫秒时，时间常数不变，尽管初始幅度A1和A2，特别是A2增加了。预脉冲期间相当的钙内流会导致更多的失活，但有趣的是，恢复以相同的速率发生。钙电流恢复的时间进程也可以用两个指数之和来拟合，其时间常数都小于钡电流恢复的时间常数。然而，当预脉冲持续时间延长时，钙电流恢复的时间常数显著增加。增加细胞外钙浓度有类似的效果。增加钡内流对恢复时间常数没有影响，钡的结果与电压依赖性膜钙通道的可逆失活门控一致。钙的结果表明钙内流增强了失活。用EGTA进行细胞内灌流在钙的情况下导致较少的失活，但对钡电流没有影响。细胞内ATP增加了钙电流的恢复速率，而细胞内钒酸盐抑制了恢复。结论是钙通道的恢复取决于钙内流和膜电位，并受到影响钙代谢的物质的调节。
