Nakahari Project of Central Research Laboratory, Osaka Medical College, Takatsuki 569-8686, Japan; Laboratory of Pharmacotherapy, Osaka University of Pharmaceutical Sciences, Takatsuki 569-1094, Japan.
Eur J Pharmacol. 2013 Dec 5;721(1-3):185-92. doi: 10.1016/j.ejphar.2013.09.037. Epub 2013 Sep 25.
Levtiracetam (Lev), an inhibitor of SV2A (synaptic vesicle protein A2), affected the ATP-dependent priming of Ca(2+)-regulated exocytosis in antral mucous cells of guinea pig. In antral mucous cells, the Ca(2+)-regulated exocytosis, which is activated by acetylcholine (ACh), consists of an initial peak that declines rapidly (initial phase) followed by a second slower decline (late phase). Dinitrophenol (DNP), which depletes ATP, inhibits the ATP-dependent priming. DNP abolished the initial phase by reducing the number of primed granules, Lev decreased the frequency of initial phase, but not in the presence of DNP. Moreover, 8-bromoguanosine 3'5'-cyclic monophosphate (8BrcGMP) accelerates the ATP-dependent priming. 8BrcGMP enhances the frequency of initial phase by increasing the number of primed granule. Lev added prior to 8BrcGMP addition decreased the frequency of initial phase, but Lev added after 8BrcGMP addition did not. Thus, Lev affected the granules in the process of priming, but it did not affect the granules already primed. Lev did not affect [Ca(2+)]i in unstimulated or ACh-stimulated antral mucous cells. Immunohistochemistry and western blotting demonstrated that SV2A exists in antral mucous cells. The results suggest that SV2A plays an essential role in maintaining the process of ATP-dependent priming in antral mucous cells. In conclusion, Lev decreases the frequency of Ca(2+)-regulated exocytosis the number of primed granules by inhibiting SV2A functions, leading to a decrease in antral mucous cells.
左乙拉西坦（Lev）是 SV2A（突触小泡蛋白 A2）的抑制剂，它影响豚鼠胃窦粘液细胞中乙酰胆碱（ACh）激活的 Ca2+调节性胞吐作用的 ATP 依赖性引发。在胃窦粘液细胞中，由乙酰胆碱（ACh）激活的 Ca2+调节性胞吐作用包括快速下降的初始峰（初始相）和第二较慢下降的后期（后期相）。二硝基苯酚（DNP）可耗尽 ATP，抑制 ATP 依赖性引发。DNP 通过减少引发颗粒的数量来消除初始相，Lev 降低了初始相的频率，但在 DNP 存在的情况下没有降低初始相的频率。此外，8-溴鸟苷 3'5'-环单磷酸（8BrcGMP）加速 ATP 依赖性引发。8BrcGMP 通过增加引发颗粒的数量来增加初始相的频率。在添加 8BrcGMP 之前添加 Lev 会降低初始相的频率，但在添加 8BrcGMP 之后添加 Lev 不会降低初始相的频率。因此，Lev 影响引发过程中的颗粒，但不影响已经引发的颗粒。Lev 对未刺激或 ACh 刺激的胃窦粘液细胞中的[Ca2+]i 没有影响。免疫组织化学和 Western 印迹表明 SV2A 存在于胃窦粘液细胞中。结果表明，SV2A 在维持胃窦粘液细胞中 ATP 依赖性引发过程中起着至关重要的作用。总之，Lev 通过抑制 SV2A 功能来减少 Ca2+调节性胞吐作用的频率和引发颗粒的数量，从而导致胃窦粘液细胞减少。
