Xiang J Z, Brammer M J, Campbell I C
Department of Neuroscience, Institute of Psychiatry, London, U.K.
Eur J Pharmacol. 1991 Jun 19;207(2):93-100. doi: 10.1016/0922-4106(91)90083-t.
The mechanisms by which quisqualate and carbachol increase intrasynaptosomal free calcium ([Ca2+]i) were studied in rat cortical synaptosomes. Quisqualate (0.01-100 microM) and carbachol (100-1000 microM) increased [Ca2+]i in Fura-2 acetoxymethyl ester (Fura-2 AM)-loaded synaptosomes. The resting level of [Ca2+]i was 118 nM. The maximum increase (55%) was produced by 10 microM quisqualate which had an EC50 of 0.2 microM. The maximum increase (28%) elicited by carbachol occurred at 1000 microM and the EC50 was 30 microM. The stimulatory effects of quisqualate on [Ca2+]i were blocked by heparin (100 I.U.) but not by staurosporine (1 microM), nifedipine (1 microM) or omega-conotoxin fraction GVIA (omega-CgTx) (0.5 microM). On the other hand, the effects of carbachol on [Ca2+]i were abolished by staurosporine, nifedipine or omega-CgTx but not by heparin. Carbachol (100 microM) also significantly increased 45Ca accumulation into either resting or K+ (30 mM)-depolarised synaptosomes and these effects were inhibited by staurosporine and nifedipine. Quisqualate (10 microM) had no effect on 45Ca accumulation under resting or depolarised conditions. When quisqualate and carbachol were used in combination, there were apparently additive effects on [Ca2+]i but not on 45Ca accumulation. It is concluded that carbachol increases [Ca2+]i by facilitating Ca2+ entry through L-type Ca2+ channels via a 1,2-diacylglycerol (DAG)-protein kinase C (PKC)-dependent pathway while quisqualate mobilizes Ca2+ from inositol 1,4,5-trisphosphate (IP3)-sensitive stores.
在大鼠皮层突触体中研究了使君子氨酸和卡巴胆碱增加突触体内游离钙（[Ca2+]i）的机制。使君子氨酸（0.01 - 100微摩尔）和卡巴胆碱（100 - 1000微摩尔）可使负载了乙酰氧基甲基酯形式的Fura-2（Fura-2 AM）的突触体中的[Ca2+]i增加。[Ca2+]i的静息水平为118纳摩尔。10微摩尔的使君子氨酸产生最大增加量（55%），其半数有效浓度（EC50）为0.2微摩尔。卡巴胆碱引起的最大增加量（28%）出现在1000微摩尔时，EC50为30微摩尔。使君子氨酸对[Ca2+]i的刺激作用被肝素（100国际单位）阻断，但不被星形孢菌素（1微摩尔）、硝苯地平（1微摩尔）或ω-芋螺毒素GVIA组分（ω-CgTx）（0.5微摩尔）阻断。另一方面，卡巴胆碱对[Ca2+]i的作用被星形孢菌素、硝苯地平或ω-CgTx消除，但不被肝素消除。卡巴胆碱（100微摩尔）也显著增加了45Ca向静息或钾离子（30毫摩尔）去极化的突触体中的积累，并且这些作用被星形孢菌素和硝苯地平抑制。使君子氨酸（10微摩尔）在静息或去极化条件下对45Ca积累没有影响。当使君子氨酸和卡巴胆碱联合使用时，对[Ca2+]i似乎有相加作用，但对45Ca积累没有。结论是，卡巴胆碱通过1,2 - 二酰基甘油（DAG） - 蛋白激酶C（PKC）依赖性途径促进钙离子通过L型钙离子通道进入，从而增加[Ca2+]i，而使君子氨酸从肌醇1,4,5 - 三磷酸（IP3）敏感储存库中动员钙离子。
