Martin C, Ashley R H
Department of Biochemistry, University of Edinburgh, UK.
Cell Calcium. 1993 Jun;14(6):427-38. doi: 10.1016/0143-4160(93)90002-n.
Many aspects of nerve cell function are controlled by cytosolic Ca2+. Intracellular organelles can sequester the cation and release it in a regulated fashion through specific ion channels including ryanodine-sensitive and inositol trisphosphate (InsP3)-activated intraneuronal Ca2+ channels. We have now used the planar bilayer technique to characterize a distinct high-conductance Ca2+ channel from brain microsomal membranes, which was not found in synaptic plasma membranes. Channel conductance in 50 mM CaCl2 is approximately 100 pS. The channel is permeable to Ca2+, Ba2+, K+ and Cs+, but it is not ideally cation-selective (PCs+:PCl- = 4:1). It opens in bursts in a steeply voltage-dependent manner, with maximal activation around zero mV. Channel activity is unaffected by caffeine or ryanodine (both of which modify the gating of ryanodine-sensitive Ca2+ channels), or by InsP3 or heparin (which act on InsP3-sensitive Ca2+ channels). omega-conotoxin GVIA, ruthenium red, amiloride and procaine all block the channel, the latter two by interacting with one or more negatively-charged binding sites in the voltage gradient within the channel pore. We suggest the channel may have a role in intracellular Ca(2+)-signalling, possibly linked to the operation of intracellular Ca2+ stores.
神经细胞功能的许多方面受胞质Ca2+调控。细胞内细胞器可以螯合这种阳离子，并通过特定离子通道以受调控的方式释放它，这些通道包括对ryanodine敏感的和由肌醇三磷酸（InsP3）激活的神经元内Ca2+通道。我们现在利用平面双层技术对一种来自脑微粒体膜的独特的高电导Ca2+通道进行了特性描述，这种通道在突触质膜中未被发现。在50 mM CaCl2中通道电导约为100 pS。该通道对Ca2+、Ba2+、K+和Cs+通透，但并非理想的阳离子选择性通道（PCa2+:PCl- = 4:1）。它以陡峭的电压依赖性方式成簇开放，在约零毫伏时达到最大激活。通道活性不受咖啡因或ryanodine（二者均可改变对ryanodine敏感的Ca2+通道的门控）、或InsP3或肝素（作用于InsP3敏感的Ca2+通道）的影响。ω-芋螺毒素GVIA、钌红、阿米洛利和普鲁卡因均可阻断该通道，后两者通过与通道孔电压梯度内的一个或多个带负电荷的结合位点相互作用来实现阻断。我们认为该通道可能在细胞内Ca(2+)信号传导中发挥作用，可能与细胞内Ca2+储存的运作有关。
