MECHANISM OF MUSCARINIC CONTROL OF THE HIGH-THRESHOLD CALCIUM CURRENT IN RABBIT SINOATRIAL NODE MYOCYTES
MECHANISM OF MUSCARINIC CONTROL OF THE HIGH-THRESHOLD CALCIUM CURRENT IN RABBIT SINOATRIAL NODE MYOCYTES
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DOI：
10.1007/bf00374956
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发表时间：
1993-04-01
影响因子：
4.5
通讯作者：
LENFANT, J
中科院分区：
文献类型：
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作者：
PETITJACQUES, J;BOIS, P;LENFANT, J
采用全细胞电压钳技术研究了乙酰胆碱（ACh）对兔心房肌细胞L型钙电流（I(Ca，L)）的作用机制。在没有先前的β -肾上腺素能刺激的情况下，乙酰胆碱在0.05-10 μ m的浓度范围内降低了基础I（Ca，L）。加入阿托品后，乙酰胆碱诱导的I（Ca，L）的减少被逆转，表明毒蕈碱受体介导了这一过程。用含有百日咳毒素的溶液孵育细胞导致乙酰胆碱作用的消除，这表明这种作用是由毒蕈碱受体激活的G蛋白介导的。用蛋白激酶抑制剂或5'-腺苷酰酰酰咪啶二磷酸（camp依赖性蛋白激酶抑制剂）透析的细胞可使基础I（Ca，L）降低约85%，并抑制乙酰胆碱的作用。在用cAMP的不可水解类似物8-溴cAMP透析的细胞中，乙酰胆碱的作用也不存在。结果表明，在基础条件下，大部分l型钙通道应被高cAMP水平和高腺苷酸环化酶活性刺激的蛋白激酶a磷酸化。乙酰胆碱对I（Ca，L）的抑制作用可能通过抑制高基础腺苷酸环化酶活性而发生，导致camp依赖性蛋白激酶刺激减少，从而导致钙通道的去磷酸化。
The mechanism of the action of acetylcholine (ACh) on the L-type calcium current (I(Ca,L)) was examined using a whole-cell voltage-clamp technique in single sino-atrial myocytes from the rabbit heart. ACh depressed basal I(Ca,L) at concentrations in the range 0.05-10 muM, without previous beta-adrenergic stimulation. The ACh-induced reduction of I(Ca,L) was reversed by addition of atropine, indicating that muscarinic receptors mediate it. Incubation of cells with a solution containing pertussis toxin led to abolition of the ACh effect, suggesting that this effect is mediated by G proteins activated by muscarinic receptors. Dialysis of cells with protein kinase inhibitor or 5'-adenylyl imidodiphosphate, inhibitors of the cAMP-dependent protein kinase, decreased basal I(Ca,L) by about 85% and suppressed the effect of ACh. The ACh effect was also absent in cells dialysed with a non-hydrolysable analogue of cAMP, 8-bromo-cAMP. The results suggest that, in basal conditions, a large part of the L-type calcium channels should be phosphorylated by protein kinase A stimulated by a high cAMP level correlated with a high adenylate cyclase activity. The depressing effect of ACh on I(Ca,L) may occur via inhibition of the high basal adenylate cyclase activity leading to a decrease of cAMP-dependent protein kinase stimulation and thus to a dephosphorylation of calcium channels.