Mediation of AMP Kinase in the Increase of Glucose Uptake in L6 Cells Induced by Activation of Imidazoline I-2 Receptors

Abstract

Recent work using radioactive tracer indicates that activation of imidazoline I2 receptor (I2R) by guanidinium derivatives may increase the glucose uptake in the skeletal muscle. However, the effect of I2R activation on nonradioactive glucose uptake is still unknown. The ability of glucose uptake in cultured L6 cells is then determined using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) as a fluorescence indicator. The changes in 5'-AMP-activated protein kinase (AMPK) expression were also identified by Western blot analysis. In the present study, 2-(2-benzofuranyl)-2-imidazoline (2-BFI) is used to stimulate I2R while 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) is applied to activate AMPK directly. Both compounds can increase 2-NBDG in L6 cells in a concentration-dependent manner. Meanwhile, compound C at concentrations sufficient to inhibit AMPK blocked this increase of glucose uptake by 2-BFI or AICAR. However, only 2-BFI-induced glucose uptake action was dose-dependently blocked by BU224, a specific I2R antagonist, in L6 cells. Moreover, AMPK phosphorylation was markedly increased by 2-BFI or AICAR in L6 cells. Similarly, only the effect of 2-BFI was attenuated by BU224 in L6 cells. Thus, we suggest that AMPK is mediated in I2R activation for increase of glucose uptake in the skeletal muscle cell and I2R will be a new target for diabetic therapy.

Characterization of the Specificity of Imidazoline I-1 Receptor Antibody for Subtype of Imidazoline Receptors In Vitro

“…In the present study, we have demonstrated that anti-NISCH antibody positively probed the imidazoline receptors on many tissues with the presence of I-2 or I-3 receptors. Also, 2-BFI increased glucose uptake through an activation of I-2 receptor [ 24 ] and this action was blockade by anti-NISCH antibody in the present study ( • ▶ Fig. 4 ).…”

“…The glucose uptake was increased by 2-BFI into L6 cells at the eff ective concentration of 10 -8 M [ 24 ] . Treatment with anti-NISCH antibody reversed this 2-BFI-induced glucose uptake in a concentration-dependent manner ( • ▶ Fig.…”

“…The medium was removed, and the cells were washed gently with phosphate buff er solution (PBS). Cells were detached from the dish by using a trypsin treatment, suspended in 0.2 mM of 2-NBDG and 2-BFI (10 − 8 M) [ 24 ] with/without anti-NISCH antibody (0.5-5 μg), and then incubated in a 37 °C water bath for 60 min in the dark. The cells were centrifuged (4 °C, 5 000 × g , 10 min) to discard the supernatant.…”

Decrease of Obesity by Allantoin via Imidazoline I1-Receptor Activation in High Fat Diet-Fed Mice

“…There are 3 types of imidazoline receptors, named as I 1 R, I 2 R and I 3 R [22, 23]. Previous studies have demonstrated that the activation of I 1 R may improve hypertension via sympathoinhibition [24]; the activation of I 2 R may improve insulin resistance via the AMP kinase pathway to enhance glucose uptake in type-2 diabetic animal models [25–27]; and the stimulation of I 3 R may stimulate insulin secretion from pancreatic β cells [28]. Although I 2 R has been reported to regulate monoamine oxidase (MAO) in the brain [29], I 3 R has not been found in the brain and is expressed mainly in the pancreas [28].…”

Discriminative stimulus effects of the imidazoline I2 receptor ligands BU224 and phenyzoline in rats

“…In acute nociception tests, although 2-BFI enhances the antinociceptive effect of morphine, BU224 has no effect but blocks 2-BFI-induced enhancement (Sanchez-Blazquez et al, 2000; Thorn et al, 2011). Indeed, BU224 is sometimes used as an I 2 receptor antagonist (Chen et al, 2014; Yang et al, 2013). These findings suggest that BU224 may be a low efficacy I 2 receptor agonist, although other mechanisms cannot be ruled out under certain conditions (Min et al, 2013).…”