Currie K P, Fox A P
The Department of Pharmacological and Physiological Sciences, The University of Chicago, Chicago, Illinois 60637, USA.
J Neurosci. 1997 Jun 15;17(12):4570-9. doi: 10.1523/JNEUROSCI.17-12-04570.1997.
Activation of N- and P/Q-type voltage-gated calcium channels triggers neurotransmitter release at central and peripheral synapses. These channels are targets for regulatory mechanisms, including inhibition by G-protein-linked receptors. Inhibition of P/Q-type channels has been less well studied than the extensively characterized inhibition of N-type channels, but it is thought that they are inhibited by similar mechanisms although possibly to a lesser extent than N-type channels. The aim of this study was to compare the inhibition of the two channel types. Calcium currents were recorded from adrenal chromaffin cells and isolated by the selective blockers omega-conotoxin GVIA (1 microM) and omega-agatoxin IVA (400 nM). The inhibition was elicited by ATP (100 microM) or intracellular application of GTP-gamma-S. It was classified as voltage-sensitive (relieved by a conditioning prepulse) or voltage-insensitive (present after a conditioning prepulse). The voltage-insensitive inhibition accounted for a 20% reduction of both currents, whereas the voltage-sensitive inhibition reduced the N-type current by 45% but the P/Q-type current by 18%. However, the voltage dependence of the inhibition, the time course of relief from inhibition during a conditioning prepulse, and the time course of reinhibition after such a prepulse showed few differences between the N- and P/Q-type channels. Assuming a simple bimolecular reaction, our data suggest that changes in the kinetics of the G-protein/channel interaction alone cannot explain the differences in the inhibition of the N- and P/Q-type calcium channels. The subtle differences in inhibition may facilitate the selective regulation of neurotransmitter release.
N型和P/Q型电压门控钙通道的激活触发中枢和外周突触处的神经递质释放。这些通道是调节机制的靶点，包括受G蛋白偶联受体的抑制。与对N型通道广泛深入的抑制研究相比，对P/Q型通道的抑制研究较少，但据认为它们受相似机制抑制，尽管程度可能低于N型通道。本研究的目的是比较这两种通道类型的抑制情况。从肾上腺嗜铬细胞记录钙电流，并通过选择性阻滞剂ω-芋螺毒素GVIA（1微摩尔）和ω-阿加毒素IVA（400纳摩尔）分离。抑制由ATP（100微摩尔）或细胞内应用GTP-γ-S引发。抑制被分类为电压敏感型（通过预处理脉冲缓解）或电压不敏感型（在预处理脉冲后存在）。电压不敏感型抑制使两种电流均降低20%，而电压敏感型抑制使N型电流降低45%，但使P/Q型电流降低18%。然而，抑制的电压依赖性、预处理脉冲期间抑制缓解的时间进程以及该脉冲后再抑制的时间进程在N型和P/Q型通道之间几乎没有差异。假设为简单的双分子反应，我们的数据表明仅G蛋白/通道相互作用动力学的变化无法解释N型和P/Q型钙通道抑制的差异。抑制的细微差异可能有助于神经递质释放的选择性调节。
