Canavanine increases glucose uptake in C2 C12 cells through the activation of imidazoline I-2B receptors

Canavanine is a guanidinium derivative that contains the basic structure of the ligand(s) of imidazoline receptor (I-R). Canavanine has been reported to activate the imidazoline I-3 receptor (I-3R) both in vivo and in vitro. Additionally, the activation of the imidazoline I-2B receptor (I-2BR) by guanidinium derivatives may increase glucose uptake. Therefore, the effect of canavanine on the I-2BR was investigated in the present study. Glucose uptake into cultured C2 C12 cells was determined using the radio-ligated tracer 2-[(14) C]-deoxy-glucose. The changes in 5' AMP-activated protein kinase (AMPK) expression were also identified using Western blotting analysis. The canavanine-induced glucose uptake was inhibited in a dose-dependent manner by BU224 (0.01-1 μmol/L), which is a specific I-2BR antagonist, in the C2 C12 cells. Additionally, the canavanine-stimulated AMPK phosphorylation and glucose transporter (GLUT4) expression were also sensitive to BU224 inhibition in the C2 C12 cells. Moreover, both canavanine-stimulated glucose uptake and AMPK phosphorylation were attenuated by high concentrations of amiloride (1-2 μmol/L), which is another established I-2BR inhibitor, in a dose-dependent manner in C2 C12 cells. Additionally, compound C abolished the canavanine-induced glucose uptake and AMPK phosphorylation at a concentration (0.1 μmol/L) sufficient to inhibit AMPK. In conclusion, these data demonstrated that canavanine has an ability to activate I-2BR through the AMPK pathway to increase glucose uptake, which indicates I-2BR as a new target for diabetic therapy.