Characterization of muscarinic receptor subtypes inhibiting Ca2+ current and M current in rat sympathetic neurons.

Muscarinic receptors mediating suppression of Ca2+ current and of M-type K+ current in rat superior cervical ganglion neurons were subclassified pharmacologically by using the muscarinic receptor antagonists pirenzepine and himbacine. Our voltage clamp experiments previously distinguished fast and slow intracellular signaling pathways coupling muscarinic receptors to calcium channels. We now establish that the fast, pertussis toxin-sensitive suppression of Ca2+ current is mediated primarily by muscarinic receptors of the M4 subtype, whereas the slow, bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetate (BAPTA)-sensitive suppression of Ca2+ current is mediated primarily by muscarinic receptors of the M1 subtype. Both actions on Ca2+ current are blocked by guanosine 5'-[beta-thio]diphosphate. Muscarinic suppression of M current is slow, BAPTA-sensitive, and mediated by receptors of the M1 subtype. Hence the two muscarinic pathways use different receptors and different guanine nucleotide binding proteins to produce different actions on channels.

在大鼠颈上神经节神经元（rat superior cervical ganglion neurons）中，介导钙电流（Ca²⁺ current）与M型钾电流（M-type K⁺ current）抑制效应的毒蕈碱受体（muscarinic receptors），可通过毒蕈碱受体拮抗剂哌仑西平（pirenzepine）与辛巴碱（himbacine）开展药理学亚型分类。本团队此前的电压钳（voltage clamp）实验已明确区分了将毒蕈碱受体与钙通道偶联的快速与慢速细胞内信号通路。本研究现已证实：对钙电流产生快速且对百日咳毒素（pertussis toxin）敏感的抑制效应，主要由M4亚型毒蕈碱受体介导；而对钙电流产生慢速且对双(2-氨基苯氧基)乙烷-N,N,N',N'-四乙酸（BAPTA）敏感的抑制效应，则主要由M1亚型毒蕈碱受体介导。上述两类对钙电流的调控作用均可被鸟苷5'-[β-硫代]二磷酸（guanosine 5'-[beta-thio]diphosphate）阻断。毒蕈碱受体对M型钾电流的抑制效应表现为慢速且对BAPTA敏感，该效应由M1亚型毒蕈碱受体介导。综上，两条毒蕈碱受体信号通路通过不同的受体与不同的鸟苷酸结合蛋白（guanine nucleotide binding proteins），对离子通道产生差异化的调控作用。