Yoshii M, Tsunoo A, Narahashi T
Department of Pharmacology, Northwestern University Medical School, Chicago, Illinois 60611.
Biophys J. 1988 Nov;54(5):885-95. doi: 10.1016/S0006-3495(88)83025-X.
The gating and permeation properties of two types of calcium channels were studied in the neuroblastoma cell line N1E-115. Calcium channel currents as carried by Ba2+ (50 mM) were recorded using the whole-cell variation of the patch electrode voltage-clamp technique. The two types of calcium channels showed similar membrane potential dependence with respect to the steady-state activation and inactivation gating properties. However, the properties of the long-lasting type II channels were shifted approximately 30 mV in the depolarizing direction compared with those of the transient type I channels. Activation of type I channels developed with a sigmoidal time course which was described by m2 kinetics, whereas the activation of type II channels was described by a single exponential function. Tail current upon repolarization followed an exponential decay in either type of calcium channels. In comparison to type I channels, the activation process of type II channels was shifted approximately 30 mV in the positive direction, while the deactivation process showed a 60 mV shift in the positive direction. The rate constants of activation obtained from the activation and deactivation processes indicated that under comparable membrane potential conditions, type II channels close 2.4 times faster than type I channels upon repolarization. When external 50 mM Ba2+ was replaced with Ca2+ or Sr2+ on the equimolar basis, the amplitudes of transient and long-lasting currents were altered without a significant change in their time courses. The ion permeability ratios determined from the maximum amplitude of the inward current were as follows: Ba2+ (1.0) = Sr2+ (1.0) greater than Ca2+ (0.7) for type I channels, and Ba2+ (1.0) greater than Sr2+ (0.7) greater than Ca2+ (0.3) for type II channels. Replacement of Ba2+ with Ca2+ caused a 10-12 mV positive shift in the current-voltage relation for type II channels. However, the shift for type I channels was much less. This suggests that negative surface charges are present around type II channels. After correction for the surface charge effect on the ion permeation, there was no significant difference between the permeability ratios of these cations for the two channel types. It was concluded that the two types of calcium channels have many common properties in their gating and permeation mechanisms despite their differential voltage sensitivity and ion selectivity.
在神经母细胞瘤细胞系N1E - 115中研究了两种类型钙通道的门控和通透特性。使用膜片钳电极电压钳技术的全细胞变体记录由Ba2 +（50 mM）携带的钙通道电流。两种类型的钙通道在稳态激活和失活门控特性方面表现出相似的膜电位依赖性。然而，与瞬时I型通道相比，持久II型通道的特性在去极化方向上大约偏移了30 mV。I型通道的激活以S形时间进程发展，由m2动力学描述，而II型通道的激活由单指数函数描述。复极化时的尾电流在两种类型的钙通道中均遵循指数衰减。与I型通道相比，II型通道的激活过程在正向方向上大约偏移30 mV，而去激活过程在正向方向上偏移60 mV。从激活和去激活过程获得的激活速率常数表明，在相当的膜电位条件下，复极化时II型通道关闭的速度比I型通道快2.4倍。当在等摩尔基础上用Ca2 +或Sr2 +替代外部50 mM Ba2 +时，瞬时和持久电流的幅度发生改变，但其时间进程没有显著变化。根据内向电流的最大幅度确定的离子通透率如下：对于I型通道，Ba2 +（1.0）= Sr2 +（1.0）> Ca2 +（0.7）；对于II型通道，Ba2 +（1.0）> Sr2 +（0.7）> Ca2 +（0.3）。用Ca2 +替代Ba2 +导致II型通道的电流 - 电压关系正向偏移10 - 12 mV。然而，I型通道的偏移要小得多。这表明II型通道周围存在负表面电荷。在校正表面电荷对离子通透的影响后，这两种阳离子对两种通道类型的通透率没有显著差异。得出的结论是，尽管这两种类型的钙通道具有不同的电压敏感性和离子选择性，但它们在门控和通透机制方面有许多共同特性。
