Ca2+ permeability of nicotinic acetylcholine receptors from rat dorsal root ganglion neurones
Ca2+ permeability of nicotinic acetylcholine receptors from rat dorsal root ganglion neurones
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DOI：
10.1113/jphysiol.2005.084871
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发表时间：
2005-05-15
影响因子：
5.5
通讯作者：
Eusebi, F
中科院分区：
文献类型：
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作者：
Fucile, S;Sucapane, A;Eusebi, F
Ca2+ 通过神经元烟碱 ACh 受体 (nAChR) 进入，调节神经组织中的许多生物过程。为了研究 nAChR 在外周感觉信号传导中的功能作用，我们测量了其在大鼠背根神经节 (DRG) 神经元中的 Ca2+ 通透性，并分析了 nAChR 介导的 Ca2+ 内流对香草酸受体 TRPV1 功能的影响。通过Ca2+成像荧光显微镜结合膜片钳技术测量流过nAChR通道的Ca2+电流分数（P-f，即Ca2+离子携带的电流的百分比）。功能性 nAChR 在成年 DRG 神经元的子集中（约占细胞的 24%）表达，根据其电容（40 +/- 3 pF）测量，通常具有小到中等大小。在大多数细胞中，ACh 会引起缓慢的脱敏电流，对同聚 nAChR 的有效拮抗剂甲基利卡乌头碱 (MLA，10 nM) 不敏感。在 15% 的 ACh 反应细胞中观察到可能由 α 7*-nAChR（即含有天然 α 7 的 nAChR）介导的快速衰减电流，其中同时存在由异聚 nAChR 介导的缓慢衰减电流。在存在 MLA 的情况下，成年 DRG 神经元的 nAChR 表现出 2.2 +/- 0.6% 的 P-f 值，在不存在 MLA 的情况下，表现出 1.9 +/- 0.6% (P > 0.1)，表明同质 MLA 敏感的 nAChR 不会促进 Ca2+ 进入成年 DRG 神经元。相反，10% 的新生儿 DRG 神经元表现出 ACh 诱发电流被 MLA 完全阻断。在这些神经元中，nAChR 显示出较大的 P-f 值 (9.5 +/- 1.5%)，表明真正的 α 7*-nAChR 的表达。最后，我们报道了成年 DRG 神经元中 Ca2+ 通过 nAChR 的流入负向调节了 TRPV1 介导的反应，这代表了烟碱激动剂对感觉神经元镇痛特性的可能机制。
Ca2+ entry through neuronal nicotinic ACh receptors (nAChRs) modulates many biological processes in nervous tissue. In order to study the functional role of nAChRs in peripheral sensory signalling, we measured their Ca2+ permeability in rat dorsal root ganglion (DRG) neurones, and analysed the effects of nAChR-mediated Ca2+ influx on the function of the vanilloid receptor TRPV1. The fractional Ca2+ current (P-f, i.e. the percentage of current carried by Ca2+ ions) flowing through nAChR channels was measured by Ca2+ imaging fluorescence microscopy in combination with the patch-clamp technique. Functional nAChRs were expressed in a subset of adult DRG neurones (about 24% of the cells), typically with small to medium size as measured by their capacitance (40 +/- 3 pF). In most cells, ACh evoked slowly desensitizing currents, insensitive to methyllycaconitine (MLA, 10 nM), a potent antagonist of homomeric nAChRs. Fast decaying currents, probably mediated by alpha 7*-nAChRs (i.e. native alpha 7-containing nAChRs), were observed in 15% of ACh-responsive cells, in which slowly decaying currents, mediated by heteromeric nAChRs, were simultaneously present. The nAChRs of adult DRG neurones exhibited a P-f value of 2.2 +/- 0.6% in the presence of MLA and 1.9 +/- 0.6% (P > 0.1) in the absence of MLA, indicating that homomeric MLA-sensitive nAChRs do not contribute to Ca2+ entry into adult DRG neurones. Conversely, 10% of neonatal DRG neurones showed ACh-evoked currents completely blocked by MLA. In these neurones, nAChRs showed a larger P-f value (9.5 +/- 1.5%), indicating the expression of bona fide alpha 7*-nAChRs. Finally, we report that Ca2+ influx through nAChRs in adult DRG neurones negatively modulated the TRPV1-mediated responses, representing a possible mechanism underlying the analgesic properties of nicotinic agonists on sensory neurones.