Kurachi Y, Nakajima T, Sugimoto T
Pflugers Arch. 1986 Nov;407(5):572-4. doi: 10.1007/BF00657521.
Effects of intracellular Mg2+ in the activation of a muscarinic K+ channel were examined in single atrial cells, using patch-recording techniques. In "cell-attached" patch recordings, acetylcholine (ACh) or adenosine (Ado), present in the pipette, activated a specific population of K+ channels. In "inside-out" patches, openings of the K+ channel by ACh or Ado diminished and did not resume until Mg2+ was added to the perfusate which contained GTP or GTP-gamma S, a non-hydrolyzable GTP analogue. Channel openings caused by GTP faded by removing Mg2+, while GTP-gamma S-induced openings persisted steadily even when both Mg2+ and GTP-gamma S were removed. In contrast to the case of GTP-induced channel openings, the GTP-gamma S-induced openings were not inhibited by the A promoter of pertussis toxin with NAD. From these observations, we concluded: Intracellular Mg2+ is essential for GTP to activate the GTP-binding protein. Deactivation of the N protein may be caused by hydrolysis of GTP to GDP. This process may not require Mg2+. During the activation by GTP analogues, the N protein may be dissociated into its subunits.
运用膜片钳记录技术，在单个心房细胞中研究了细胞内镁离子（Mg2+）对毒蕈碱型钾通道激活的影响。在“细胞贴附式”膜片钳记录中，移液管中的乙酰胆碱（ACh）或腺苷（Ado）可激活特定群体的钾通道。在“内面向外式”膜片中，ACh或Ado引起的钾通道开放减少，并且在向含有GTP或GTP-γS（一种不可水解的GTP类似物）的灌流液中添加Mg2+之前不会恢复。去除Mg2+会使由GTP引起的通道开放消失，而即使同时去除Mg2+和GTP-γS，GTP-γS诱导的开放仍稳定持续。与GTP诱导的通道开放情况相反，GTP-γS诱导的开放不受百日咳毒素A启动子与NAD的抑制。基于这些观察结果，我们得出结论：细胞内Mg2+对于GTP激活GTP结合蛋白至关重要。N蛋白的失活可能是由GTP水解为GDP所致。此过程可能不需要Mg2+。在由GTP类似物激活期间，N蛋白可能会解离成其亚基。
