Bezprozvanny I, Scheller R H, Tsien R W
Department of Molecular and Cellular Physiology, Stanford University Medical Center, California 94305, USA.
Nature. 1995 Dec 7;378(6557):623-6. doi: 10.1038/378623a0.
Rapid and reliable synaptic transmission depends upon the close proximity of voltage-gated calcium channels and neurotransmitter-containing vesicles in the presynaptic terminal. Although it is clear that a local Ca2+ rise conveys the crucial signal from Ca2+ channels to the exocytotic mechanism, little is known about whether communication ever proceeds in the opposite direction, from the release machinery to Ca2+ channels. To look for such signalling, we examined the interaction of various types of voltage-gated Ca2+ channels with syntaxin, a presynaptic membrane protein of relative molecular mass 35,000 which may play a key part in synaptic vesicle docking and fusion and which interacts strongly with N-type Ca2+ channels. Here we report that co-expression of syntaxin 1A with N-type channels in Xenopus oocytes sharply decreases the availability of these channels. This is due to the stabilization of channel inactivation rather than to a simple block or lack of channel expression, because it is overcome by strong hyperpolarization. Deletion of syntaxin's carboxy-terminal transmembrane domain abolishes its functional effect on Ca2+ channels. Syntaxin produced a similar effect on Q-type Ca2+ channels encoded by alpha 1A but not on L-type Ca2+ channels. Thus, the syntaxin effect is specific for Ca2+ channel types that participate in fast transmitter release in the mammalian central nervous system. We hypothesize that, in addition to acting as a vesicle-docking site, syntaxin may influence presynaptic Ca2+ channels, opposing Ca2+ entry where it is not advantageous, but allowing it at release sites where synaptic vesicles have become docked and/or ready for fusion.
快速而可靠的突触传递依赖于突触前终末中电压门控钙通道与含神经递质囊泡的紧密靠近。虽然很明显局部Ca2+升高将关键信号从Ca2+通道传递到胞吐机制，但对于信号传递是否曾以相反方向进行，即从释放机制到Ca2+通道，却知之甚少。为了寻找这种信号传递，我们研究了各种类型的电压门控Ca2+通道与 syntaxin（一种相对分子质量为35000的突触前膜蛋白，它可能在突触囊泡对接和融合中起关键作用，并且与N型Ca2+通道强烈相互作用）之间的相互作用。在此我们报告，在非洲爪蟾卵母细胞中 syntaxin 1A与N型通道共表达会急剧降低这些通道的可用性。这是由于通道失活的稳定化，而不是简单的阻断或通道表达缺失，因为强超极化可克服这一现象。删除 syntaxin 的羧基末端跨膜结构域可消除其对Ca2+通道的功能影响。Syntaxin 对由α1A编码的Q型Ca2+通道产生类似作用，但对L型Ca2+通道无此作用。因此，syntaxin 的作用对参与哺乳动物中枢神经系统快速递质释放的Ca2+通道类型具有特异性。我们推测，除了作为囊泡对接位点外，syntaxin 可能会影响突触前Ca2+通道，在不利的地方阻止Ca2+内流，但在突触囊泡已对接和/或准备融合的释放位点允许Ca2+内流。
