Fasolato C, Hoth M, Penner R
Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Federal Republic of Germany.
J Biol Chem. 1993 Oct 5;268(28):20737-40.
Calcium influx in electrically non-excitable cells is regulated by the filling state of intracellular calcium stores. Depletion of stores activates plasma membrane channels that are voltage-independent and highly selective for Ca2+ ions. We report here that the activation of plasma membrane Ca2+ currents induced by depletion of Ca2+ stores requires a diffusible cytosolic factor that washes out with time when dialyzing cells in the whole-cell configuration of the patch-clamp technique. The activation of calcium release-activated calcium current (ICRAC) by ionomycin- or inositol 1,4,5-trisphosphate-induced store depletion is blocked by guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) and guanyl-5'-yl imidodiphosphate, non-hydrolyzable analogs of GTP, suggesting the involvement of a GTP-binding protein. The inhibition by GTP gamma S occurs at a step prior to the activation of ICRAC and is prevented by the addition of GTP. We conclude that the activation mechanism of depletion-induced Ca2+ influx encompasses a GTP-dependent step, possibly involving an as yet unidentified small GTP-binding protein.
电非兴奋性细胞中的钙内流受细胞内钙库充盈状态的调节。钙库耗竭会激活质膜通道，这些通道不依赖电压，且对Ca2+离子具有高度选择性。我们在此报告，Ca2+库耗竭诱导的质膜Ca2+电流激活需要一种可扩散的胞质因子，当在膜片钳技术的全细胞配置中对细胞进行透析时，该因子会随时间被洗脱。离子霉素或肌醇1,4,5-三磷酸诱导的钙库耗竭对钙释放激活钙电流（ICRAC）的激活被鸟苷5'-3-O-（硫代）三磷酸（GTPγS）和鸟苷-5'-亚基亚氨基二磷酸（GTP的非水解类似物）所阻断，这表明涉及一种GTP结合蛋白。GTPγS的抑制作用发生在ICRAC激活之前的一个步骤，并且通过添加GTP可以防止这种抑制。我们得出结论，耗竭诱导的Ca2+内流的激活机制包括一个GTP依赖性步骤，可能涉及一种尚未鉴定的小GTP结合蛋白。
