Rondé P, Nichols R A
Department of Pharmacology, MCP-Hahnemann School of Medicine, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19129, USA.
J Neurochem. 1998 Mar;70(3):1094-103. doi: 10.1046/j.1471-4159.1998.70031094.x.
The serotonin 5-HT3 receptor, a ligand-gated ion channel, has previously been shown to be present on a subpopulation of brain nerve terminals, where, on activation, the 5-HT3 receptors induce Ca2+ influx. Whereas postsynaptic 5-HT3 receptors induce depolarization, being permeant to Na+ and K+, the basis of presynaptic 5-HT3 receptor-induced calcium influx is unknown. Because the small size of isolated brain nerve terminals (synaptosomes) precludes electrophysiological measurements, confocal microscopic imaging has been used to detect calcium influx into them. Application of 100 nM 1-(m-chlorophenyl)biguanide (mCPBG), a highly specific 5-HT3 receptor agonist, induced increases in internal free Ca2+ concentration ([Ca2+]i) and exocytosis in a subset of corpus striatal synaptosomes. mCPBG-induced increases in [Ca2+]i ranged from 1.3 to 1.6 times over basal values and were inhibited by 10 nM tropisetron, a potent and highly specific 5-HT3 receptor antagonist, but were insensitive to the removal of external free Na+ (substituted with N-methyl-D-glucamine), to prior depolarization induced on addition of 20 mM K+, or to voltage-gated Ca2+ channel blockade by 10 microM Co2+/Cd2+ or by 1 microM omega-conotoxin MVIIC/1 microM oemga-conotoxin GVIA/200 nM agatoxin TK. In contrast, the Ca2+ influx induced by 5-HT3 receptor activation in NG108-15 cells by 1 microM mCPBG was substantially reduced by 10 microM Co2+/Cd2+ and was completely blocked by 1 microM nitrendipine, an L-type Ca2+ channel blocker. We conclude that in contrast to the perikaryal 5-HT3 receptors, presynaptic 5-HT3 receptors appear to be uniquely calcium-permeant.
血清素5-HT3受体是一种配体门控离子通道，先前已证明其存在于一部分脑神经终末上，激活时，5-HT3受体可诱导Ca2+内流。虽然突触后5-HT3受体可诱导去极化，对Na+和K+通透，但突触前5-HT3受体诱导钙内流的机制尚不清楚。由于分离出的脑神经终末（突触体）体积小，无法进行电生理测量，因此共聚焦显微镜成像已被用于检测钙向其中的内流。应用100 nM 1-(间氯苯基)双胍（mCPBG），一种高度特异性的5-HT3受体激动剂，可诱导纹状体突触体亚群内游离Ca2+浓度（[Ca2+]i）升高和胞吐作用增强。mCPBG诱导的[Ca2+]i升高幅度为基础值的1.3至1.6倍，并被10 nM托烷司琼抑制，托烷司琼是一种强效且高度特异性的5-HT3受体拮抗剂，但对去除细胞外游离Na+（用N-甲基-D-葡糖胺替代）、添加20 mM K+诱导的先前去极化或10 μM Co2+/Cd2+或1 μM ω-芋螺毒素MVIIC/1 μM ω-芋螺毒素GVIA/200 nM蜘蛛毒素TK对电压门控Ca2+通道的阻断均不敏感。相比之下，1 μM mCPBG在NG108-15细胞中激活5-HT3受体诱导的Ca2+内流被10 μM Co2+/Cd2+显著降低，并被1 μM尼群地平完全阻断，尼群地平是一种L型Ca2+通道阻滞剂。我们得出结论，与胞体5-HT3受体不同，突触前5-HT3受体似乎具有独特的钙通透性。
