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

Abstract

Abstract. 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 Ser 473 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-HT 2A receptors, it decreased the particulate protein level and reciprocally increased the soluble protein level of 5-HT 2A receptors in a concentration-dependent manner. These results demonstrate that insulin can induce the internalization of 5-HT 2A receptors from the plasma membrane to the cytoplasm. The insulin-induced internalization of 5-HT 2A 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-HT 2A receptors and the production of nitric oxide via the PI3-K/Akt pathway.

5HT2Aand5HT2Nelson1, Harrod2, Lamping3 2012Experimental Diabetes Research232120View full textAdd to dashboardCite

“…Increased levels of insulin induce internalization of 5HT 2A receptors in smooth muscle of saphenous veins [44]. Insulin levels in db/db mice are dependent upon age with increases peaking 5–10 times higher than non-diabetic mice at 4-5 weeks of age and subsequently declining til they are normal at 25 weeks of age [45–47].…”

Angiotensin II, as well as 5-hydroxytriptamine, is a potent vasospasm inducer of saphenous vein graft for coronary artery bypass grafting in patients with diabetes mellitus

“…At Kuwabara Clinic, portions of the SV were sectioned from each patient as a surgical treatment for varix of the lower extremity, and only the non-distended areas were used for the experiments. The small SV segments were transported and their constrictive responses were measured as described previously [11] , [12] . In brief, isolated vessels were placed in modified Krebs buffer, which had been previously aerated with 95% O 2 and 5% CO 2 , and transported promptly to our laboratory.…”

“…Frozen SV rings were crushed with manual mill SK-200 (Tokken, inc.) and suspended in transmembrane protein extraction buffer 1 (ProteoExtract Transmembrane Protein Extraction Kit; Calbiochem-Novabiochem). Preparation for the membrane fractions and Western blot analysis was performed as described previously [11] . Equal amounts of protein (5.5 μg per lane) were separated by SDS-10% polyacrylamide gel electrophoresis and transferred onto a polyvinylidene difluoride membrane Hybond-P (GE Healthcare Japan).…”

5-Hydroxytryptamine Receptors as Targets for Drug Therapies of Vascular-Related Diseases

“…77) We recently reported that insulin induced vasodilation in a concentration-dependent manner in endothelium-denuded human SVs that had been preconstricted with 5-HT. 78) Furthermore, insulin caused internalization of 5-HT 2A receptors also in a concentration-dependent manner. A large number of studies suggest that insulin induces vasodilation via the production of NO in endothelial cells and a reduction of Ca 2+ concentrations in vascular smooth muscle cells.…”