School of Pharmaceutical Science, China Medical University, Shenyang, China.
J Pharmacol Sci. 2010;112(3):310-9. doi: 10.1254/jphs.09282fp. Epub 2010 Mar 2.
The L-type Ca(2+) channel (Ca(V)1.2) shows clear Ca(2+)-dependent facilitation and inactivation. Here we have examined the effects of calmodulin (CaM) and Ca(2+) on Ca(2+) channel in guinea-pig ventricular myocytes in the inside-out patch mode, where rundown of the channels was controlled. At a free [Ca(2+)] of 0.1 microM, CaM (0.15, 0.7, 1.4, 2.1, 3.5, and 7.0 microM) + ATP (2.4 mM) induced channel activities of 27%, 98%, 142%, 222%, 65%, and 20% relative to the control activity, respectively, showing a bell-shaped relationship. Similar results were observed at a free [Ca(2+)] <0.01 microM or with a Ca(2+)-insensitive mutant, CaM(1234), suggesting that apoCaM may induce facilitation and inactivation of the channel activity. The bell-shaped curve of CaM was shifted to the lower concentration side with increasing [Ca(2+)]. A simple model for CaM- and Ca(2+)-dependent modulations of the channel activity, which involves two CaM-binding sites, was proposed. We suggest that both apoCaM and Ca(2+)/CaM can induce facilitation and inactivation of Ca(V)1.2 Ca(2+) channels and that the basic role of Ca(2+) is to accelerate CaM-dependent facilitation and inactivation.
L 型钙通道（Ca(V)1.2）表现出明显的 Ca2+依赖性易化和失活。在此，我们通过在膜片钳内面向模式下，检查了豚鼠心室肌细胞中钙调蛋白（CaM）和 Ca2+对 Ca2+通道的影响，在该模式下，通道的衰减受到控制。在游离 [Ca2+] 为 0.1 μM 时，CaM（0.15、0.7、1.4、2.1、3.5 和 7.0 μM）+ATP（2.4 mM）分别诱导通道活性增加 27%、98%、142%、222%、65%和 20%，相对于对照活性，呈现钟形关系。在游离 [Ca2+] <0.01 μM 或使用 Ca2+ 不敏感突变体 CaM(1234)时观察到类似的结果，表明无 Ca2+ 的 CaM 可能诱导通道活性的易化和失活。随着 [Ca2+] 的增加，CaM 的钟形曲线向较低浓度侧移动。提出了一种简单的模型，用于 CaM 和 Ca2+-依赖性调节通道活性，该模型涉及两个 CaM 结合位点。我们认为，无 Ca2+ 的 CaM 和 Ca2+/CaM 都可以诱导 Ca(V)1.2 Ca2+通道的易化和失活，而 Ca2+ 的基本作用是加速 CaM 依赖性的易化和失活。
