Grassi F, Giovannelli A, Fucile S, Eusebi F
Department of Experimental Medicine, University of Rome, Italy.
Pflugers Arch. 1993 Mar;422(6):591-8. doi: 10.1007/BF00374007.
In cultured mouse C2C12 myotubes, digital Ca2+ imaging fluorescence microscopy using the acetoxymethyl ester of Fura-2, Fura-2-AM, showed that, in the absence of extracellular Ca2+, acetylcholine (ACh) and nicotine, but not muscarine, raised the intracellular concentration of Ca2+ ([Ca2+]i) by about tenfold. ACh-induced Ca2+ mobilization was prevented by thapsigargin, a drug known to deplete inositol 1,4,5-trisphosphate (InsP3)-sensitive stores, and was concomitant with InsP3 accumulation. Caffeine, which releases Ca2+ from the ryanodine-sensitive stores of the sarcoplasmic reticulum, did not interfere with the ACh-induced [Ca2+]i increase. Ca2+ mobilization was also inhibited when myotubes were depolarized by high K+, or when extracellular Na+ was omitted. Nicotinic ACh receptor (nAChR) stimulation lowered intracellular pH with a time course slower than the [Ca2+]i increase. Possible mechanisms linking the current flowing through the nAChR pore to [Ca2+]i increase are discussed.
在培养的小鼠C2C12肌管中，使用Fura-2的乙酰氧基甲酯（Fura-2-AM）进行数字Ca2+成像荧光显微镜观察显示，在细胞外无Ca2+的情况下，乙酰胆碱（ACh）和尼古丁可使细胞内Ca2+浓度（[Ca2+]i）升高约10倍，而毒蕈碱则无此作用。毒胡萝卜素（一种已知可耗尽肌醇1,4,5-三磷酸（InsP3）敏感储存库的药物）可阻止ACh诱导的Ca2+动员，且ACh诱导的Ca2+动员与InsP3积累同时发生。咖啡因可从肌浆网的兰尼碱敏感储存库释放Ca2+，但不干扰ACh诱导的[Ca2+]i升高。当肌管用高K+去极化或去除细胞外Na+时，Ca2+动员也受到抑制。烟碱型ACh受体（nAChR）刺激可使细胞内pH降低，其时间进程比[Ca2+]i升高慢。文中讨论了将流经nAChR孔道的电流与[Ca2+]i升高联系起来的可能机制。
