Institut für Pharmakologie und Toxikologie, Technische Universität München, Munich, Germany.
Am J Physiol Gastrointest Liver Physiol. 2009 Oct;297(4):G834-9. doi: 10.1152/ajpgi.00095.2009. Epub 2009 Jul 23.
cGMP-dependent protein kinase I (cGKI) induces relaxation of smooth muscle via several pathways that include inhibition of intracellular Ca(2+) signaling and/or involve activation of myosin phosphatase. In the present study, we investigated these mechanisms comparatively in colon and jejunum longitudinal smooth muscle from mice. In simultaneous recordings from colon muscle, 8-bromo-cGMP (8-Br-cGMP) reduced both carbachol-induced tension and carbachol-induced increase in intracellular Ca(2+) concentration (Ca(2+)). These effects of 8-Br-cGMP were absent in colon from mice carrying a mutated inositol-1,4,5 trisphosphate receptor I-associated G kinase substrate (IRAG) gene or lacking cGKI. However, in jejunum, 8-Br-cGMP reduced carbachol-induced tension but did not change corresponding Ca(2+) signals. This setting was also observed in jejunum from mice carrying a mutated IRAG gene, whereas no response to 8-Br-cGMP was observed in jejunum from mice lacking cGKI. After inhibition of phosphatase activity by calyculin A, 8-Br-cGMP did not relax jejunum but still relaxed colon muscle. In Western blot analysis, 8-Br-cGMP reduced the signal for phosphorylated MYPT-1 in carbachol-stimulated jejunum but not in colon. These results suggest that cGMP/cGKI signaling differentially inhibits contraction in the muscles investigated: in jejunum, inhibition is performed without changing Ca(2+) and is dependent on phosphatase activity, whereas in colon, inhibition is mediated by inhibition of Ca(2+) signals.
环鸟苷酸依赖性蛋白激酶 I（cGKI）通过多种途径诱导平滑肌松弛，包括抑制细胞内 Ca(2+)信号和/或涉及肌球蛋白磷酸酶的激活。在本研究中，我们比较研究了来自小鼠的结肠和空肠纵行平滑肌中的这些机制。在结肠肌肉的同步记录中，8-溴-cGMP（8-Br-cGMP）降低了乙酰胆碱诱导的张力和乙酰胆碱诱导的细胞内 Ca(2+)浓度增加(Ca(2+))。在携带突变肌醇-1,4,5 三磷酸受体 I 相关 G 激酶底物（IRAG）基因或缺乏 cGKI 的小鼠的结肠中，8-Br-cGMP 没有这些作用。然而，在空肠中，8-Br-cGMP 降低了乙酰胆碱诱导的张力，但没有改变相应的Ca(2+)信号。在携带突变 IRAG 基因的小鼠的空肠中也观察到了这种情况，而在缺乏 cGKI 的小鼠的空肠中则没有对 8-Br-cGMP 的反应。在钙调神经磷酸酶活性被 calyculin A 抑制后，8-Br-cGMP 不能松弛空肠，但仍能松弛结肠肌肉。在 Western blot 分析中，8-Br-cGMP 降低了在乙酰胆碱刺激的空肠中磷酸化 MYPT-1 的信号，但在结肠中没有。这些结果表明，cGMP/cGKI 信号在研究的肌肉中以不同的方式抑制收缩：在空肠中，抑制是在不改变Ca(2+)的情况下进行的，并且依赖于磷酸酶活性，而在结肠中，抑制是通过抑制Ca(2+)信号介导的。
