Novel I(1)-Imidazoline Agonist S43126 Augment Insulin Secretion in Min6 Cells

The I(1)-imidazoline receptor is a novel drug target for hypertension and insulin resistance which are major disorders associated with Type II diabetes. In the present study, we examined the effects of a novel imidazoline agonist S43126 on calcium fluxes and insulin secretion from Min6 β-cells. We also examined the effects of S43126 on the induction of IRAS, and phosphorylation of components in the I(1)-imidazoline signaling pathways, namely ERK and PKB. Min6 β-cells were treated with varying doses of S43126 [10(−8)M to 10(−5)M] for various time (5–60mins). S43126 at higher dose [10(−5)M] stimulated insulin secretion under elevated glucose concentration compared to basal. In addition, insulin secretion and Ca(2+) influx mediated by S43126 [10(−5)M] were decreased following co-treatment with efaroxan (I(1)-antagonist) and nifedipine (L-type voltage-gated Ca(2+)-channel blocker) at various times (5–60mins). Furthermore, S43126 at [10(−5)M] increased Ca(2+) oscillation, [Ca(2+)] and (45)Ca(2+) uptake in a time and dose-dependent manner. Moreover, Western blot analysis of treated samples showed that S43126 caused an increased protein expression of IRAS as well as phosphorylation of both ERK1/2 and PKB in a concentration-dependent manner. We conclude that S43126 exerts its insulinotropic effect in a glucose dependent manner by a mechanism involving L-type calcium channels and imidazoline I(1)-receptors.