Shin Min-Chul, Nonaka Kiku, Yamaga Toshitaka, Wakita Masahito, Akaike Hironari, Akaike Norio
Research Division for Life Science, Kumamoto Health Science University , Kumamoto , Japan.
Research Division for Clinical Pharmacology, Medical Corporation, Juryo Group, Kumamoto Kinoh Hospital , Kumamoto , Japan.
J Neurophysiol. 2018 Sep 1;120(3):1264-1273. doi: 10.1152/jn.00571.2017. Epub 2018 Jun 13.
The current electrophysiological study investigated the functional roles of high- and low-voltage-activated Ca channel subtypes on glutamatergic small mossy fiber nerve terminals (SMFTs) that synapse onto rat hippocampal CA3 neurons. Experiments combining both the "synapse bouton" preparation and single-pulse focal stimulation technique were performed using the conventional whole cell patch configuration under voltage-clamp conditions. Nifedipine, at a high concentration, and BAY K 8644 inhibited and facilitated the glutamatergic excitatory postsynaptic currents (eEPSCs) that were evoked by 0.2-Hz stimulation, respectively. However, these drugs had no effects on spontaneous EPSCs (sEPSCs). Following the use of a high stimulation frequency of 3 Hz, however, nifedipine markedly inhibited eEPSCs at the low concentration of 0.3 µM. Moreover, ω-conotoxin GVIA and ω-agatoxin IVA significantly inhibited both sEPSCs and eEPSCs. Furthermore, SNX-482 slightly inhibited eEPSCs. R(-)-efonidipine had no effects on either sEPSCs or eEPSCs. It was concluded that glutamate release from SMFTs depends largely on Ca entry through N- and P/Q-type Ca channels and, to a lesser extent, on R-type Ca channels. The contribution of L-type Ca channels to eEPSCs was small at low-firing SMFTs but more significant at high-firing SMFTs. T-type Ca channels did not appear to be involved in neurotransmission at SMFTs. NEW & NOTEWORTHY Action potential-evoked glutamate release from small mossy fiber nerve terminals (SMFTs) that synapse onto rat hippocampal CA3 neurons is regulated by high-threshold but not low-threshold Ca channel subtypes. The functional contribution mainly depends on N- and P/Q-type Ca channels and, to a lesser extent, on R-type Ca channels. However, in SMFTs stimulated at a high 3-Hz frequency, L-type Ca channels contributed significantly to the currents. The present results are consistent with previous findings from fluorometric studies of large mossy fiber boutons.
当前的电生理研究探讨了高电压激活和低电压激活的钙通道亚型对与大鼠海马CA3神经元形成突触的谷氨酸能小苔藓纤维神经末梢（SMFTs）的功能作用。在电压钳制条件下，采用传统的全细胞膜片钳配置，结合“突触小体”制备和单脉冲局灶刺激技术进行实验。高浓度的硝苯地平和BAY K 8644分别抑制和促进了0.2 Hz刺激诱发的谷氨酸能兴奋性突触后电流（eEPSCs）。然而，这些药物对自发性突触后电流（sEPSCs）没有影响。然而，在使用3 Hz的高刺激频率后，低浓度（0.3 μM）的硝苯地平显著抑制了eEPSCs。此外，ω-芋螺毒素GVIA和ω-阿加毒素IVA显著抑制了sEPSCs和eEPSCs。此外，SNX-482轻微抑制了eEPSCs。R(-)-依福地平对sEPSCs和eEPSCs均无影响。得出的结论是，SMFTs释放谷氨酸主要依赖于通过N型和P/Q型钙通道的钙内流，在较小程度上依赖于R型钙通道。L型钙通道对低发放频率的SMFTs的eEPSCs贡献较小，但对高发放频率的SMFTs贡献更大。T型钙通道似乎不参与SMFTs的神经传递。新发现与值得注意的点 与大鼠海马CA3神经元形成突触的小苔藓纤维神经末梢（SMFTs）动作电位诱发的谷氨酸释放受高阈值而非低阈值钙通道亚型调节。其功能贡献主要取决于N型和P/Q型钙通道，在较小程度上取决于R型钙通道。然而，在以3 Hz高频率刺激的SMFTs中，L型钙通道对电流有显著贡献。目前的结果与先前对大型苔藓纤维小体的荧光研究结果一致。
