Kaneda Makoto, Ito Koichi, Morishima Yosuke, Shigematsu Yasuhide, Shimoda Yukio
Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan.
J Neurophysiol. 2007 Jun;97(6):4225-34. doi: 10.1152/jn.01022.2006. Epub 2007 Apr 11.
Recent studies have shown that cholinergic amacrine cells possess unique membrane properties. However, voltage-gated ionic channels in cholinergic amacrine cells have not been characterized systematically. In this study, using electrophysiological and immunohistochemical techniques, we examined voltage-gated ionic channels in a transgenic mouse line the cholinergic amacrine cells of which were selectively labeled with green fluorescent protein (GFP). Voltage-gated K(+) currents contained a 4-aminopyridine-sensitive current (A current) and a tetraethylammonium-sensitive current (delayed rectifier K(+) current). Voltage-gated Ca(2+) currents contained a omega-conotoxin GVIA-sensitive component (N-type) and a omega-Aga IVA-sensitive component (P/Q-type). Tetrodotoxin-sensitive Na(+) currents and dihydropyridine-sensitive Ca(2+) currents (L-type) were not observed. Immunoreactivity for the Na channel subunit (Pan Nav), the K channel subunits (the A-current subunits [Kv. 3.3 and Kv 3.4]) and the Ca channel subunits (alpha1(A) [P/Q-type], alpha1(B) [N-type] and alpha1(C) [L-type]) was detected in the membrane fraction of the mouse retina by Western blot analysis. Immunoreactivity for the Kv. 3.3, Kv 3.4, alpha1(A) [P/Q-type], and alpha1(B) [N-type] was colocalized with the GFP signals. Immunoreactivity for alpha1(C) [L-type] was not colocalized with the GFP signals. Immunoreactivity for Pan Nav did not exist on the membrane surface of the GFP-positive cells. Our findings indicate that signal propagation in cholinergic amacrine cells is mediated by a combination of two types of voltage-gated K(+) currents (the A current and the delayed rectifier K(+) current) and two types of voltage-gated Ca(2+) currents (the P/Q-type and the N-type) in the mouse retina.
最近的研究表明，胆碱能无长突细胞具有独特的膜特性。然而，胆碱能无长突细胞中的电压门控离子通道尚未得到系统的表征。在本研究中，我们使用电生理和免疫组织化学技术，在一个转基因小鼠品系中检测电压门控离子通道，该品系的胆碱能无长突细胞被绿色荧光蛋白（GFP）选择性标记。电压门控钾电流包含一个4-氨基吡啶敏感电流（A电流）和一个四乙铵敏感电流（延迟整流钾电流）。电压门控钙电流包含一个ω-芋螺毒素GVIA敏感成分（N型）和一个ω-银环蛇毒素IVA敏感成分（P/Q型）。未观察到河豚毒素敏感的钠电流和二氢吡啶敏感的钙电流（L型）。通过蛋白质免疫印迹分析在小鼠视网膜的膜部分检测到钠通道亚基（泛钠通道）、钾通道亚基（A电流亚基[Kv. 3.3和Kv 3.4]）和钙通道亚基（α1(A)[P/Q型]、α1(B)[N型]和α1(C)[L型]）的免疫反应性。Kv. 3.3、Kv 3.4、α1(A)[P/Q型]和α1(B)[N型]的免疫反应性与GFP信号共定位。α1(C)[L型]的免疫反应性与GFP信号未共定位。GFP阳性细胞的膜表面不存在泛钠通道的免疫反应性。我们的研究结果表明，在小鼠视网膜中，胆碱能无长突细胞中的信号传播是由两种类型的电压门控钾电流（A电流和延迟整流钾电流）和两种类型的电压门控钙电流（P/Q型和N型）共同介导的。
