Bradykinin potentiates insulin-stimulated glucose uptake and enhances insulin signal through the bradykinin B2 receptor in dog skeletal muscle and rat L6 myoblasts

Abstract

Previously we demonstrated that bradykinin infusion could increase glucose uptake into dog peripheral tissues, and that bradykinin could potentiate insulin-induced glucose uptake through glucose transporter 4 (GLUT4) translocation in dog adipocytes. However, skeletal muscle is the predominant affected insulin-stimulated glucose uptake in dog skeletal muscle and myotubes transformed from rat 1,6 myoblasts. The bradykinin receptor binding studies revealed that dog skeletal muscle and rat 1.6 myoblasts possessed significant numbers of bradykinin receptors (K(d) = 88 and 76 pmol/l. B(max) = 82.5 and 20fmol/mg protein respectively). An RT-PCR treverse transcriptase-polymerase chain reaction) amplification showed mRNA specific for bradykinin B2 receptor in both cells. Bradykinin significantly increased 2-deoxyglucose uptake in isolated muscle and 1.6 myoblasts in the presence of insulin (10-7 mol/h) in a dose-dependent manner, but not in the absence of insulin. Bradykinin also enhanced insulin-stimulated GLUT4 translocation, and insulin-phosphorylation of insulin receptor β submit and insulin receptor substrate-1 (IRS-1) without affecting the binding affinities or numbers of cell surface insulin receptors in both cells. It is concluded that bradykinin could potentiate the insulin-induced glucose uptake through GLI T4 translocation in dog skeletal muscle and rat 1.6 myoblasts. This effect could be explained by the potency of bradykinin to upregulate the insulin receptor tyrosine kinase activity which stimulates phosphorylation of IRS-1, followed by an increase in GLUT4 translocation.