Dual Effect of ATP on Glucose-Induced Insulin Secretion in HIT-T15 Cells

Objectives: The study investigated the dual effect of purinergic nucleotides on the secretion of insulin from pancreatic beta cells. Methods: The level of insulin secretion in HTT-T15 cells of static incubation was measured using a radioimmunoassay. Results: The adenine nucleotides reduced the level of glucose-induced insulin secretion in a concentration-dependent manner, and the relative potency order (IC50; mu M) was BzATP (6.9) > ATP (20.4) >= alpha, beta-methylene ATP (23.3) >= 2-methylthio-ATP (24.9). Suramin and PPADS (200 mu M), which are blockers of the purinergic receptors, had a little influence on the activity of ATP. However, the inhibitory effect of ATP was reversed by preincubation with oxidized ATP (200 mu M), which is a P2X(7) antagonist. The level of insulin secretion in these preincubated cells exposed to the purinergic nucleotides increased in the following order: ATP > alpha, beta-methylene ATP > 2-methylthio-ATP. A pretreatment with foskolin and PDBu (100 nM) potentiated the increasing effect of ATP on insulin secretion. The Western blotting showed the expression of P2X(7) and P2Y(11) receptors. Conclusions: Purinergic stimulation has inhibitory activity on glucose-dependent insulin secretion through the activation of the P2X(7) receptor, whereas it has enhancing effect through the activation of the P2Y(11) receptor in HIT-T15 cells.