Department of Physiology and Biophysics, VCU Program in Enteric Neuromuscular Sciences, Virginia Commonwealth University, Box 980551, Richmond, VA, 23298, United States.
Department of Physiology and Biophysics, VCU Program in Enteric Neuromuscular Sciences, Virginia Commonwealth University, Box 980551, Richmond, VA, 23298, United States.
Peptides. 2019 Feb;112:48-55. doi: 10.1016/j.peptides.2018.11.007. Epub 2018 Nov 30.
The insulinotropic effects of the incretin hormone, glucagon-like peptide-1 (GLP-1) are mediated via GLP-1 receptors (GLP-1R) present on pancreatic β cells. GLP-1 causes a decrease in the motility of stomach and intestine which involves both central and peripheral nervous systems. The expression and function of GLP-1R in gastrointestinal smooth muscle, however, are not clear. Muscle strips and isolated muscle cells were prepared from mouse colon and the effect of GLP-1(7-36) amide on acetylcholine (ACh)-induced contraction was measured. Muscle cells in culture were used to identify the expression of GLP-1R and the signaling pathways activated by GLP-1(7-36) amide. GLP-1R was expressed in the mucosal and non-mucosal tissue preparations derived from colon, and in smooth muscle cell cultures devoid of other cells such as enteric neurons. In colonic muscle strips, the addition of GLP-1(7-36) amide caused dose-dependent inhibition of acetylcholine-induced contractions. The effect of GLP-1(7-36) amide was partly inhibited by the neuronal blocker tetrodotoxin and nitric oxide (NO) synthase inhibitor l-NNA suggesting both NO-dependent neural and NO-independent direct effects on smooth muscle. In isolated colonic smooth muscle cells, GLP-1(7-36) amide caused an increase in Gα activity, cAMP levels, and PKA activity, and inhibited ACh-induced contraction. The effect of GLP-1(7-36) amide on Gα activity and cAMP levels was blocked by NF449, an inhibitor of Gα and the effect of GLP-1(7-36) amide on contraction was blocked by NF449 and myristoylated PKI, an inhibitor of PKA. We conclude that colonic smooth muscle cells express GLP-1R, and GLP-1(7-36) amide inhibits acetylcholine-induced contraction via GLP-1R coupled to the Gα/cAMP/PKA pathway.
肠促胰岛素激素胰高血糖素样肽-1（GLP-1）的促胰岛素作用是通过胰腺β细胞上存在的 GLP-1 受体（GLP-1R）介导的。GLP-1 可降低胃和肠道的运动，这涉及中枢和外周神经系统。然而，GLP-1R 在胃肠道平滑肌中的表达和功能尚不清楚。从小鼠结肠中制备肌肉条和分离的肌肉细胞，并测量 GLP-1(7-36)酰胺对乙酰胆碱（ACh）诱导的收缩的影响。使用培养的肌肉细胞来鉴定 GLP-1R 的表达以及 GLP-1(7-36)酰胺激活的信号通路。GLP-1R 在源自结肠的粘膜和非粘膜组织制剂以及在没有其他细胞（如肠神经元）的平滑肌细胞培养物中表达。在结肠肌肉条中，GLP-1(7-36)酰胺的添加导致乙酰胆碱诱导的收缩呈剂量依赖性抑制。GLP-1(7-36)酰胺的作用部分被神经元阻滞剂河豚毒素和一氧化氮（NO）合酶抑制剂 l-NNA 抑制，表明对平滑肌有依赖于 NO 的神经和不依赖于 NO 的直接作用。在分离的结肠平滑肌细胞中，GLP-1(7-36)酰胺引起 Gα 活性、cAMP 水平和 PKA 活性增加，并抑制 ACh 诱导的收缩。GLP-1(7-36)酰胺对 Gα 活性和 cAMP 水平的作用被 NF449 阻断，NF449 是 Gα 的抑制剂，GLP-1(7-36)酰胺对收缩的作用被 NF449 和 PKA 的抑制剂 myristoylated PKI 阻断。我们得出结论，结肠平滑肌细胞表达 GLP-1R，GLP-1(7-36)酰胺通过与 Gα/cAMP/PKA 通路偶联的 GLP-1R 抑制乙酰胆碱诱导的收缩。
