Koh D S, Hille B
Department of Physiology and Biophysics, University of Washington, Seattle 98195-7290, USA.
Proc Natl Acad Sci U S A. 1997 Feb 18;94(4):1506-11. doi: 10.1073/pnas.94.4.1506.
Many neuromodulators inhibit N-type Ca2+ currents via G protein-coupled pathways in acutely isolated superior cervical ganglion (SCG) neurons. Less is known about which neuromodulators affect release of norepinephrine (NE) at varicosities and terminals of these neurons. To address this question, we used carbon fiber amperometry to measure catecholamine secretion evoked by electrical stimulation at presumed sites of high terminal density in cultures of SCG neurons. The pharmacological properties of action potential-evoked NE release paralleled those of N-type Ca2+ channels: Release was completely blocked by Cd2+ or omega-conotoxin GVIA, reduced 50% by 10 microM NE or 62% by 2 microM UK-14,304, an alpha2-adrenergic agonist, and reduced 63% by 10 microM oxotremorine M (Oxo-M), a muscarinic agonist. Consistent with action at M2 or M4 receptor subtypes, Oxo-M could be antagonized by 10 microM muscarinic antagonists methoctramine and tropicamide but not by pirenzepine. After overnight incubation with pertussis toxin, inhibition by UK-14,304 and Oxo-M was much reduced. Other neuromodulators known to inhibit Ca2+ channels in these cells, including adenosine, prostaglandin E2, somatostatin, and secretin, also depressed secretion by 34-44%. In cultures treated with omega-conotoxin GVIA, secretion dependent on L-type Ca2+ channels was evoked with long exposure to high K+ Ringer's solution. This secretion was not sensitive to UK-14,304 or Oxo-M. Evidently, many neuromodulators act on the secretory terminals of SCG neurons, and the depression of NE release at terminals closely parallels the membrane-delimited inhibition of N-type Ca2+ currents in the soma.
许多神经调质通过G蛋白偶联途径抑制急性分离的颈上神经节（SCG）神经元中的N型Ca2+电流。关于哪些神经调质会影响这些神经元曲张体和终末去甲肾上腺素（NE）的释放，我们所知较少。为了解决这个问题，我们使用碳纤维安培法来测量在SCG神经元培养物中假定的高终末密度部位进行电刺激所诱发的儿茶酚胺分泌。动作电位诱发的NE释放的药理学特性与N型Ca2+通道的特性相似：释放被Cd2+或ω-芋螺毒素GVIA完全阻断，10μM NE使其减少50%，2μM UK-14,304（一种α2-肾上腺素能激动剂）使其减少62%，10μM毒蕈碱激动剂氧化震颤素M（Oxo-M）使其减少63%。与作用于M2或M4受体亚型一致，Oxo-M可被10μM毒蕈碱拮抗剂甲溴东莨菪碱和托吡卡胺拮抗，但不能被哌仑西平拮抗。在用百日咳毒素过夜孵育后，UK-14,304和Oxo-M的抑制作用大大降低。已知在这些细胞中抑制Ca2+通道的其他神经调质，包括腺苷、前列腺素E2、生长抑素和促胰液素，也使分泌减少34 - 44%。在用ω-芋螺毒素GVIA处理的培养物中，长时间暴露于高钾林格氏溶液可诱发依赖L型Ca2+通道的分泌。这种分泌对UK-14,304或Oxo-M不敏感。显然，许多神经调质作用于SCG神经元的分泌终末，终末NE释放的抑制与胞体中N型Ca2+电流的膜限定抑制密切平行。
