Insulin Induces Internalization of the Plasma Membrane 5-Hydroxytryptamine2A (5-HT2A) Receptor in the Isolated Human Endothelium-Denuded Saphenous Vein via the Phosphatidylinositol 3-Kinase Pathway

• Published in: Journal of Pharmacological Sciences 2012, Vol.118(2), pp.178-185
• Main Authors: Kanai, Tasuku, Kuwabara, Masachika, Tanaka-Totoribe, Naoko, Nakamura, Eisaku, Matsuo, Yasuko, Gamoh, Shuji, Suzuki, Akito, Asada, Yujiro, Hisa, Hiroaki, Yamamoto, Ryuichi
• Format: Article
• Language: English
• Subjects: Cell Membrane - drug effects; Cell Membrane - metabolism; diabetes mellitus (DM); Dose-Response Relationship, Drug; Endothelium, Vascular - drug effects; Endothelium, Vascular - metabolism; Humans; Hypoglycemic Agents - administration & dosage; Hypoglycemic Agents - pharmacology; Insulin - administration & dosage; Insulin - pharmacology; insulin-induced vasorelaxation; internalization of 5-HT2A receptor; nitric oxide (NO); Nitric Oxide - metabolism; Phosphatidylinositol 3-Kinases - metabolism; Proto-Oncogene Proteins c-akt - metabolism; Receptor, Serotonin, 5-HT2A - metabolism; saphenous vein (SV); Saphenous Vein - drug effects; Saphenous Vein - metabolism; Serotonin - metabolism; Serotonin - pharmacology; Signal Transduction - drug effects; Vasoconstriction - drug effects; Vasodilation - drug effects
• ISSN: 1347-8613; 1347-8648
• DOI: 10.1254/jphs.11172FP

The aim of this study was to investigate the relaxant effect of insulin on the 5-hydroxytryptamine (5-HT)-induced constriction of the human endothelium-denuded saphenous vein (SV) and its signal transduction pathway. During the 5-HT-induced sustained constriction of vessels, insulin induced vasorelaxation in a concentration-dependent manner. This insulin-induced vasorelaxation was partially attenuated by L-NAME, a nitric oxide synthase (NOS) inhibitor, and was abolished by wortmannin, a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Insulin increased the Ser473 phosphorylation of Akt. Endothelial NOS and inducible NOS protein expressions were observed in SV smooth muscle when insulin induced relaxation of SV vessels preconstricted with 5-HT. Although insulin did not affect the total protein level of 5-HT2A receptors, it decreased the particulate protein level and reciprocally increased the soluble protein level of 5-HT2A receptors in a concentration-dependent manner. These results demonstrate that insulin can induce the internalization of 5-HT2A receptors from the plasma membrane to the cytoplasm. The insulin-induced internalization of 5-HT2A receptors was abolished by wortmannin but was not affected by L-NAME. These results suggest that the relaxant effect of insulin on 5-HT-induced vasoconstriction is mediated in part by the internalization of plasma membrane 5-HT2A receptors and the production of nitric oxide via the PI3-K/Akt pathway.