FAST AND SLOW GATING BEHAVIOR OF SINGLE CALCIUM CHANNELS IN CARDIAC-CELLS - RELATION TO ACTIVATION AND INACTIVATION OF CALCIUM-CHANNEL CURRENT
FAST AND SLOW GATING BEHAVIOR OF SINGLE CALCIUM CHANNELS IN CARDIAC-CELLS - RELATION TO ACTIVATION AND INACTIVATION OF CALCIUM-CHANNEL CURRENT
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DOI：
10.1007/bf00640910
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发表时间：
1986-03-01
影响因子：
4.5
通讯作者：
TRAUTWEIN, W
中科院分区：
文献类型：
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作者：
CAVALIE, A;PELZER, D;TRAUTWEIN, W
(1)通过记录从成年豚鼠心脏酶法分离的单心室细胞的细胞附着膜片的单 Ca 通道活性，检查了稳定和逐步去极化期间的 Ca 通道门控行为。单通道记录是通过改进的膜片钳技术（Hamill 等人，1981）在移液器中使用 90 mM Ba 进行的。（2）在逐步去极化时，在整体中定期观察到两种类型的电流记录：（1）不同长度的 Ca 通道活动痕迹（以具有单一幅度的紧密间隔的内向电流短脉冲形式），以及（2）没有任何可检测到的空白扫描单通道开放。 Ca 通道活动的记录显示出在钳位脉冲开始时出现开放的明显趋势，随后是长时间的静默。空白扫描似乎反映了 Ca 通道无法打开的一种或多种情况。相应的系综平均电流I(t)表现出一个快速上升阶段，到达峰值后缓慢衰减。(3)在稳定去极化过程中，对所有打开和关闭寿命分布的动力学分析揭示了所有打开时间的单指数概率密度分布函数。相比之下，需要两个以上的指数项才能准确描述所有关闭寿命的频率分布。对应于两个分离良好的快速关闭时间分量，各个 Ca 通道开口被分组为开口突发。爆发行为反映了快速门控转换，并且与 Ca 通道在两个短暂关闭状态和一个打开状态之间的波动有关。这种快速门控通过 Ca2+ 通道进入至少一种长期关闭状态而终止，与快速循环相比，退出该状态的速度较慢。结果，开口爆发进一步分组为爆发簇，簇行为与 Ca 通道动力学中的缓慢门控转变有关。（4）第一延迟的双相频率分布（在进入打开状态之前，由通过两个短暂关闭状态的转变而产生）叠加在整体平均电流上升阶段的一阶时间导数上，I(t)，在阶跃去极化上。所有星团寿命的单指数分布函数的时间常数与维持去极化期间 I(t) 的下降阶段相匹配。因此，通道打开概率的降低和由此产生的 I(t) 下降似乎是由于 Ca2+ 通道转变为长寿命的第三类关闭状态。 (5) 在一系列试验中，Ca2+ 通道的响应性在正保持电势下下降，并且由于系综中空白单通道电流记录数量的增加，对条件去极化电势呈 S 形依赖性。具有通道开口以及空白扫描的迹线倾向于在调节去极化时形成连续的单通道电流记录序列。只有在打开状态或两个短暂关闭状态占用期间施加命令脉冲，Ca 通道才可激活。如果长期关闭状态已经被调节电位占据……
(1)The Ca-channel gating behaviour during steady and stepwise depolarization was examined in recordings of single Ca-channel activity from cell-attached membrane patches of single ventricular cells isolated enzymatically from hearts of adult guinea pigs. The single-channel recordings were performed by means of the improved patch-clamp technique (Hamill et al. 1981) with 90 mM Ba in the pipettes.(2)Upon step depolarization, two types of current records were regularly observed in the ensembles: (1) traces with Ca-channel activity (in the form of closely-spaced brief pulses of inward current with a unitary amplitude) of various length, and (2) blank sweeps without any detectable single-channel opening. The records with Ca-channel activity show a distinct tendency for openings to occur towards the beginning of the clamp pulse, followed by long periods of silence. The blank sweeps seem to reflect a condition or conditions where the Ca channel is unavailable for opening. The corresponding ensemble mean currentI(t)displayed a rapid rising phase to its peak followed by a slow decay.(3)During steady depolarization, kinetic analysis of the distributions of all open and shut lifetimes revealed a monoexponential probability density distribution function of all open times. By contrast, more than two exponential terms were required for an accurate description of the frequency distribution of all shut lifetimes. Corresponding to the two well-separated fast closed time components, individual Ca-channel openings were grouped into bursts of openings. The bursting behaviour reflected fast gating transitions and was related to the fluctuations of the Ca channel between two short-lived closed states and one open state. This fast gating was terminated by the entrance of the Ca channel into at least one long-lived closed state, exit from which was slow in comparison to the rapid cycling. As consequence, bursts of openings were further grouped together in clusters of bursts, the cluster behaviour being related to slow gating transitions in the kinetics of the Ca channel.(4)The biphasic frequency distribution of the first latencies (resulting from the transit through the two short-lived shut states, before the open state is entered) superimposed on the first time derivative of the rising phase of the ensemble mean current,I(t), upon step depolarization. The time constant of the monoexponential distribution function of all cluster lifetimes matched the declining phase ofI(t)during maintained depolarization. Thus, the decrease of the probability of channel opening and the resulting decline ofI(t)seemed to be due to a transition of the Ca channel into the long-lived third class of shut state(s).(5)The responsiveness of the Ca channel in a series of trials decreased at positive holding potentials with a sigmoidal dependence on the potential of the conditioning depolarization due to an increasing number of blank single-channel current records within the ensembles. Traces with channel openings as well as blank sweeps tended to form sequences of consecutive single-channel current records upon conditioning depolarization. The Ca channel was only activatable, if a command pulse was applied during the occupancy of either the open state or the two short-lived shut states. If the long-lived shut state(s) was already occupied at the conditioning potential …