Hochstrate P, Schlue W R
Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, Germany.
Glia. 1995 Sep;15(1):43-53. doi: 10.1002/glia.440150106.
The effect of cholinergic agonists and antagonists on the intracellular free Ca2+ concentration ([Ca2+]i) of leech neuropile glial cells was investigated by use of iontophoretically injected fura-2. In neuropile glial cells, cholinergic agonists induced a marked increase in [Ca2+]i that was inhibited by d-tubocurarine, alpha-bungarotoxin, strychnine, and atropine. The efficacy of the various agonists and antagonists indicates that the [Ca2+]i increase is mediated by the nicotinic acetylcholine (ACh) receptors that have been characterized previously in these cells by using electrophysiological methods. In the presence of high agonist concentrations, [Ca2+]i partly recovered, suggesting that the ACh receptors desensitize. The [Ca2+]i increase induced by cholinergic agonists was abolished in Ca2(+)-free solution, which indicates that it is caused by Ca2+ influx from the external medium. The agonist-induced [Ca2+]i increase was partly preserved in Na(+)-free solution, whereas the agonist-induced membrane depolarization was strongly suppressed. The agonist-induced [Ca2+]i increase was also partly preserved in the presence of 5 mM Ni2+, which almost abolished the K(+)-induced [Ca2+]i increase mediated by voltage-dependent Ca2+ channels. It is concluded that at low agonist concentrations the [Ca2+]i increase in leech neuropile glial cells is mediated exclusively by the ion channels associated with the nicotinic ACh receptors. At high agonist concentrations, voltage-dependent [Ca2+]i increase in leech neuropile glial cells is mediated exclusively by the ion channels associated with the nicotinic ACh receptors. At high agonist concentrations, voltage-dependent Ca2+ channels activated by the concomitant membrane depolarization also contribute to the agonist-induced Ca2+ influx.
通过离子电泳注入fura-2，研究了胆碱能激动剂和拮抗剂对水蛭神经纤维胶质细胞细胞内游离Ca2+浓度（[Ca2+]i）的影响。在神经纤维胶质细胞中，胆碱能激动剂诱导[Ca2+]i显著增加，这被d-筒箭毒碱、α-银环蛇毒素、士的宁和阿托品所抑制。各种激动剂和拮抗剂的作用效果表明，[Ca2+]i的增加是由烟碱型乙酰胆碱（ACh）受体介导的，此前已通过电生理方法在这些细胞中对该受体进行了表征。在高激动剂浓度存在的情况下，[Ca2+]i部分恢复，这表明ACh受体发生了脱敏。胆碱能激动剂诱导的[Ca2+]i增加在无Ca2+溶液中消失，这表明它是由外部介质中的Ca2+内流引起的。激动剂诱导的[Ca2+]i增加在无Na+溶液中部分保留，而激动剂诱导的膜去极化则受到强烈抑制。在5 mM Ni2+存在的情况下，激动剂诱导的[Ca2+]i增加也部分保留，而5 mM Ni2+几乎完全消除了由电压依赖性Ca2+通道介导的K+诱导的[Ca2+]i增加。得出的结论是，在低激动剂浓度下，水蛭神经纤维胶质细胞中[Ca2+]i的增加完全由与烟碱型ACh受体相关的离子通道介导。在高激动剂浓度下，水蛭神经纤维胶质细胞中由电压依赖性[Ca2+]i增加完全由与烟碱型ACh受体相关的离子通道介导。在高激动剂浓度下，伴随膜去极化激活的电压依赖性Ca2+通道也有助于激动剂诱导的Ca2+内流。
