Artalejo C R, Perlman R L, Fox A P
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Neuron. 1992 Jan;8(1):85-95. doi: 10.1016/0896-6273(92)90110-y.
Previous studies have identified two components of whole-cell Ca2+ current in bovine chromaffin cells. The "standard" component was activated by single depolarizations, while "facilitation" could be activated by large prepulses or repetitive depolarizations. Neither current component was sensitive to changes in holding potential between -100 and -50 mV; thus neither appeared to be carried by N-type Ca2+ channels. We now report that the facilitation Ca2+ current is insensitive to omega-conotoxin GVIA (omega-CgTx), but that the toxin blocks approximately 50% of the standard Ca2+ current. In some cells the toxin blocks all of the standard Ca2+ current, in others about half of the current, while in others it has no effect. Kinetic differences in current activation are observed after toxin application. These results suggest that the standard component of chromaffin cell Ca2+ current is composed of two pharmacologically distinct channels-one is omega-CgTx sensitive and the other is not. Two kinetically distinct types of 14 pS Ca2+ channels that may correspond to the omega-CgTx-sensitive and -insensitive components were observed in single-channel experiments. Because omega-CgTx blocked Ca2+ channels that were not inactivated by a depolarized holding potential, the commonly used Ca2+ channel categorization scheme may be inadequate to describe the Ca2+ channels found in chromaffin cells.
先前的研究已经确定了牛嗜铬细胞全细胞Ca2+电流的两个组成部分。“标准”成分由单次去极化激活，而“易化”可由大的预脉冲或重复去极化激活。两种电流成分对-100至-50 mV之间的钳制电位变化均不敏感；因此，两者似乎都不是由N型Ca2+通道介导的。我们现在报告，易化Ca2+电流对ω-芋螺毒素GVIA（ω-CgTx）不敏感，但该毒素可阻断约50%的标准Ca2+电流。在一些细胞中，毒素可阻断所有的标准Ca2+电流，在另一些细胞中可阻断约一半的电流，而在其他细胞中则没有作用。应用毒素后可观察到电流激活的动力学差异。这些结果表明，嗜铬细胞Ca2+电流的标准成分由两种药理学上不同的通道组成——一种对ω-CgTx敏感，另一种不敏感。在单通道实验中观察到两种动力学上不同类型的14 pS Ca2+通道，它们可能分别对应于对ω-CgTx敏感和不敏感的成分。由于ω-CgTx可阻断未因去极化钳制电位而失活的Ca2+通道，因此常用的Ca2+通道分类方案可能不足以描述嗜铬细胞中发现的Ca2+通道。
