Ammälä C, Berggren P O, Bokvist K, Rorsman P
Department of Medical Physics, Gothenburg University, Sweden.
Pflugers Arch. 1992 Jan;420(1):72-7. doi: 10.1007/BF00378643.
Pretreatment of pancreatic beta cells with pertussis toxin resulted in a 30% increase in peak whole-cell Ca2+ currents recorded in the absence of exogenous intracellular guanine nucleotides. Intracellular application of 90 microM GTP[gamma S], by liberation from a caged precursor, resulted in 40% reduction of the peak Ca2+ current irrespective of whether the current was carried by Ca2+ or Ba2+. Effects on the delayed outward K+ current were small and restricted to a transient Ca(2+)-dependent K+ current component. Inhibition by GTP[gamma S] of the Ca2+ current was not mimicked by standard GTP and could not be prevented either by pretreatment with pertussis toxin or by inclusion of GDP[beta S] or cyclic AMP in the intracellular medium. The inhibitory effect of GTP[gamma S] could be counteracted by a prepulse to a large depolarizing voltage. A similar effect of a depolarizing prepulse was observed in control cells with no exogenous guanine nucleotides. These observations indicate that inhibition of beta cell Ca2+ current by G protein activation results from direct interaction with the channel and does not involve second-messenger systems. Our findings also suggest that the beta cell Ca2+ current is subject to resting inhibition by G proteins.
用百日咳毒素对胰腺β细胞进行预处理，在无外源细胞内鸟嘌呤核苷酸的情况下记录到的全细胞Ca2+电流峰值增加了30%。通过从笼状前体释放，在细胞内施加90微摩尔的GTP[γS]，无论电流是由Ca2+还是Ba2+携带，都会导致Ca2+电流峰值降低40%。对延迟外向K+电流的影响较小，且仅限于短暂的Ca(2+)依赖性K+电流成分。标准GTP不能模拟GTP[γS]对Ca2+电流的抑制作用，用百日咳毒素预处理或在细胞内培养基中加入GDP[βS]或环磷酸腺苷也不能阻止这种抑制作用。GTP[γS]的抑制作用可以通过预脉冲至大的去极化电压来抵消。在没有外源鸟嘌呤核苷酸的对照细胞中也观察到了去极化预脉冲的类似作用。这些观察结果表明，G蛋白激活对β细胞Ca2+电流的抑制作用是由于与通道的直接相互作用，而不涉及第二信使系统。我们的研究结果还表明，β细胞Ca2+电流受到G蛋白的静息抑制。
