Toth P T, Shekter L R, Ma G H, Philipson L H, Miller R J
Department of Pharmacological and Physiological Sciences, The University of Chicago, Illinois 60637, USA.
J Neurosci. 1996 Aug 1;16(15):4617-24. doi: 10.1523/JNEUROSCI.16-15-04617.1996.
We examined the properties and regulation of Ca channels resulting from the expression of human alpha1B and alpha1E subunits stably expressed in KEK293 cells. The ancillary subunits beta1B and alpha2/delta were also stably expressed in these cell lines. Ca currents in alpha1B-expressing cells had the properties of N-type currents. Ca currents in cells expressing alpha1E exhibited a novel profile that was similar to the properties of the "R type" Ca current. Introduction of GTP-gamma-S into alpha1B cells greatly enhanced the extent of prepulse facilitation of the Ca current, whereas it had only a very small effect in alpha1E-expressing cells. Activation of somatostatin receptors endogenous to HEK293 cells or kappa opioid receptors, expressed in the cells after transfection, inhibited Ca currents in alpha1B-expressing cells. This inhibition was blocked by pertussis toxin and was partially relieved by a depolarizing prepulse. In contrast, no inhibitory effects were noted in cells expressing alpha1E channels under the same circumstances. HEK293 cells normally contained G-proteins from all of the four major families. Inhibition of Ca currents by kappa agonists in alpha1B-expressing cells was enhanced slightly by the cotransfection of several G-protein alpha subunits. kappa agonists, however, had no effect in alpha1E-containing cells, even after overexpression of different G-protein alpha-subunits. In summary, these results demonstrate that there is a large difference in the susceptibility of alpha1B- and alpha1E-based Ca channels to regulation by G-proteins. This is so despite the fact that the two types of Ca channels show substantial similarities in their primary sequences.
我们研究了在KEK293细胞中稳定表达的人α1B和α1E亚基所产生的钙通道的特性及调控情况。辅助亚基β1B和α2/δ在这些细胞系中也稳定表达。表达α1B的细胞中的钙电流具有N型电流的特性。表达α1E的细胞中的钙电流呈现出一种新的特征，类似于“R型”钙电流的特性。向表达α1B的细胞中引入GTP-γ-S极大地增强了钙电流预脉冲易化的程度，而在表达α1E的细胞中其作用非常小。激活HEK293细胞内源性的生长抑素受体或转染后在细胞中表达的κ阿片受体，可抑制表达α1B的细胞中的钙电流。这种抑制被百日咳毒素阻断，并且通过去极化预脉冲可部分缓解。相比之下，在相同情况下，表达α1E通道的细胞中未观察到抑制作用。HEK293细胞通常含有来自所有四个主要家族的G蛋白。在表达α1B的细胞中，几种G蛋白α亚基的共转染略微增强了κ激动剂对钙电流的抑制作用。然而，即使在不同G蛋白α亚基过表达后，κ激动剂对含有α1E的细胞也没有影响。总之，这些结果表明，基于α1B和α1E的钙通道对G蛋白调控的敏感性存在很大差异。尽管这两种类型的钙通道在其一级序列上有很大相似性，但情况依然如此。
