Study on enhancement of neuronal calcium channel activities by nootropic agents

采用全细胞膜片钳技术研究促智剂（吡咯烷酮衍生物）对NG108-15细胞神经元钙通道的影响。Nefiracetam （DM-9384）是一种新开发的促脑药，在低浓度1muM的情况下，将Ca通道电流的高压激活的持久组分增加了两倍，而不影响低压激活的瞬时组分。剂量-反应关系呈钟形曲线，在1mum处达到峰值。其他促智药物的作用类似，但效果较弱，其顺序为尼非拉西坦>阿尼拉西坦>奥拉西坦>吡拉西坦。二丁基环AMP (1 mM)，环AMP的类似物，也增强了电流，而奈非西坦没有进一步增加电流，反之亦然。l型钙通道阻滞剂硝苯地平（10mum）可显著降低奈非西坦增强的电流。其余n型电流也略有增加（高达1.5倍）。非特异性蛋白激酶抑制剂H-7 （100 muM）阻止了奈非西坦的这些促进作用。百日咳毒素（500 ng/ml, bbb20 h）灭活抑制g蛋白（Go/Gi）后，细胞对奈非西坦明显不敏感。结果表明，益智药物可能通过抑制g蛋白和可能的amp依赖性循环过程的调节，增强神经元l型Ca通道的活性。

Effects of nootropic agents (pyrrolidone derivatives) on neuronal calcium (Ca) channels were studied in NG108-15 cells using the whole-cell patch-clamp technique. Nefiracetam (DM-9384), a newly-developed nootropic agent, increased a high voltage-activated, long-lasting component of Ca channel currents two-fold at a low concentration of 1muM without affecting a low voltage-activated, transient component. The dose-response relationship yielded a bell-shaped curve with a peak at 1 muM.Similar, but less potent effects were observed by other nootropic agents in the sequence of nefiracetam > aniracetam > oxiracetam > piracetam. Dibutyryl cyclic AMP (1 mM), an analogue of cyclic AMP, also enhanced the currents, which were not further increased by nefiracetam, or vice versa. The currents enhanced by nefiracetam were markedly reduced by nifedipine (10 muM), an L-type Ca channel blocker. The remaining N-type currents also showed a slightly increase (up to 1.5-fold). These facilitatory actions of nefiracetam were prevented by the non-specific protein kinase inhibitor, H-7 (100 muM). Cells treated with pertussis toxin (500 ng/ml, >20 h) to inactivate inhibitory G-proteins (Go/Gi) were apparently insensitive to nefiracetam. The results suggest that the nootropic agents may enhance the activity of neuronal L-type Ca channels under the regulation of inhibitory G-proteins and possibly, cyclic AMP-dependent processes.