Sunouchi Takaaki, Suzuki Kimiaki, Nakayama Koichi, Ishikawa Tomohisa
Department of Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka City, Shizuoka, Japan.
Pflugers Arch. 2008 Jun;456(3):573-9. doi: 10.1007/s00424-008-0463-z. Epub 2008 Feb 1.
We have previously shown that NO has stimulatory and inhibitory effects on insulin secretion at low and high concentrations, respectively. The present study investigated effects of NO on K ATP channels of rat beta cells by patch clamp analysis to elucidate the mechanism for the dual effect. NOC7 at 0.5 microM suppressed K ATP channels activated by diazoxide in the cell-attached and perforated whole-cell modes but failed to suppress them in the inside-out mode. The inhibitory effect in the cell-attached mode was abolished by the soluble guanylate cyclase inhibitor ODQ and by the protein kinase G inhibitor KT5823. Moreover, 0.5 microM NOC7 failed to suppress the channel activity in the presence of the mitochondrial uncoupler FCCP. In contrast, 10 microM NOC7 activated K ATP channels in the cell-attached and perforated whole-cell modes, although it had no effect on the channels in the inside-out mode. The K ATP currents evoked by 10 microM NOC7 in the cell-attached mode were not inhibited by ODQ. The dual effect of NOC7 at 0.5 and 10 microM was observed in the same patch. Taken together, these results suggest that low-concentration NO exerts an inhibitory effect on K ATP channels of beta cells, which is induced through the cGMP/protein kinase G pathway, whereas high-concentration NO activates K ATP channels through the mechanism independent of cGMP.
我们之前已经表明，一氧化氮（NO）在低浓度和高浓度时分别对胰岛素分泌具有刺激和抑制作用。本研究通过膜片钳分析研究了NO对大鼠β细胞KATP通道的影响，以阐明这种双重作用的机制。0.5微摩尔的NOC7在细胞贴附式和穿孔全细胞模式下抑制了由二氮嗪激活的KATP通道，但在膜外翻式模式下未能抑制它们。细胞贴附式模式下的抑制作用被可溶性鸟苷酸环化酶抑制剂ODQ和蛋白激酶G抑制剂KT5823消除。此外，在存在线粒体解偶联剂FCCP的情况下，0.5微摩尔的NOC7未能抑制通道活性。相反，10微摩尔的NOC7在细胞贴附式和穿孔全细胞模式下激活了KATP通道，尽管它对膜外翻式模式下的通道没有影响。10微摩尔NOC7在细胞贴附式模式下诱发的KATP电流未被ODQ抑制。在同一片膜上观察到了0.5微摩尔和10微摩尔NOC7的双重作用。综上所述，这些结果表明，低浓度的NO对β细胞的KATP通道发挥抑制作用，这是通过cGMP/蛋白激酶G途径诱导的，而高浓度的NO通过独立于cGMP的机制激活KATP通道。
