Yamada M, Jahangir A, Hosoya Y, Inanobe A, Katada T, Kurachi Y
Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905.
J Biol Chem. 1993 Nov 25;268(33):24551-4.
A pertussis toxin-sensitive G protein (GK) links muscarinic cholinergic and A1-purinergic receptors with an inwardly rectifying K+ (KACh) channel in cardiac atrial cell membranes. Although the beta gamma subunits of pertussis toxin-sensitive G proteins (G beta gamma) have been reported to fully activate this channel, it is not known whether exogenously applied G beta gamma interacts with the KACh channel through the same mechanism as the active subunit of endogenous GK (GK*). We examined in inside-out patches the relationship between the concentration of GTP and KACh channel activity with or without preactivation of the channels by either GTP gamma S (guanosine 5'-3-O-(thio)triphosphate) or G beta gamma purified from bovine brain. In the control, KACh channels were activated by intracellular GTP (with acetylcholine in the pipette) in a positive cooperative manner (Hill coefficient approximately 2.5). As the channels were preactivated by GTP gamma S to progressively higher levels, the GTP channel activity relationship shifted more to the left, but the Hill coefficients of the curves remained the same. The same changes were observed when KACh channels were preactivated with brain G beta gamma. These results indicate that endogenous GK* and exogenous G beta gamma share a common molecular mechanism to activate the KACh channel.
一种对百日咳毒素敏感的G蛋白（GK）将毒蕈碱型胆碱能受体和A1-嘌呤能受体与心房肌细胞膜上的内向整流钾通道（KACh通道）相连接。尽管已有报道称百日咳毒素敏感G蛋白的βγ亚基（Gβγ）可完全激活该通道，但尚不清楚外源性应用的Gβγ是否通过与内源性GK活性亚基（GK*）相同的机制与KACh通道相互作用。我们在膜外翻片中研究了GTP浓度与KACh通道活性之间的关系，通道分别通过GTPγS（鸟苷5'-3-O-（硫代）三磷酸）或从牛脑纯化的Gβγ预激活或未预激活。在对照中，KACh通道被细胞内GTP（移液管中加入乙酰胆碱）以正协同方式激活（希尔系数约为2.5）。随着通道被GTPγS预激活至更高水平，GTP与通道活性的关系向左偏移更多，但曲线的希尔系数保持不变。当KACh通道用脑Gβγ预激活时，也观察到相同的变化。这些结果表明，内源性GK*和外源性Gβγ共享激活KACh通道的共同分子机制。
