2-(2-imidazolin-2-yl)-1-phenyl-1h-indole and decamethrin

Capacitance measurements were used to investigate the molecular mechanisms by which imidazoline compounds inhibit glucagon release in rat pancreatic alpha-cells. The imidazoline compound phentolamine reversibly decreased depolarization-evoked exocytosis >80% without affecting the whole-cell Ca(2+) current. During intracellular application through the recording pipette, phentolamine produced a concentration-dependent decrease in the rate of exocytosis (IC(50) = 9.7 microm). Another imidazoline compound, RX871024, exhibited similar effects on exocytosis (IC(50) = 13 microm). These actions were dependent on activation of pertussis toxin-sensitive G(i2) proteins but were not associated with stimulation of ATP-sensitive K(+) channels or adenylate cyclase activity. The inhibitory effect of phentolamine on exocytosis resulted from activation of the protein phosphatase calcineurin and was abolished by cyclosporin A and deltamethrin. Exocytosis was not affected by intracellular application of specific alpha(2), I(1), and I(2) ligands. Phentolamine reduced glucagon release (IC(50) = 1.2 microm) from intact islets by 40%, an effect abolished by pertussis toxin, cyclosporin A, and deltamethrin. These data suggest that imidazoline compounds inhibit glucagon secretion via G(i2)-dependent activation of calcineurin in the pancreatic alpha-cell. The imidazoline binding site is likely to be localized intracellularly and probably closely associated with the secretory granules.

Topics: Adenylate Cyclase Toxin; Animals; Calcineurin; Cells, Cultured; Clorgyline; Cyclosporine; Cystamine; Diazoxide; Exocytosis; Glucagon; GTP-Binding Protein alpha Subunit, Gi2; GTP-Binding Protein alpha Subunits, Gi-Go; Imidazoles; Indoles; Islets of Langerhans; Male; Membrane Potentials; Nitriles; Oligodeoxyribonucleotides, Antisense; Pertussis Toxin; Phentolamine; Potassium Channels; Proto-Oncogene Proteins; Pyrethrins; Rats; Rats, Inbred Lew; Virulence Factors, Bordetella

Imidazoline compounds have been considered for the treatment of type 2 diabetes. We have now investigated the effects of imidazolines on interleukin (IL)-1beta-induced beta-cell apoptosis and the signal transduction pathways involved. Inhibition of Ca2+ influx into beta-cells by D-600, a blocker of voltage-gated L-type Ca2+ channels, suppressed IL-1beta-induced apoptosis. Our data show that calcineurin, Ca2+/calmodulin-dependent serine/threonine protein phosphatase 2B, is responsible for the effect of Ca2+ on beta-cell apoptosis. We also demonstrate that IL-1beta-mediated apoptosis correlates with expression of inducible nitric oxide synthase (iNOS) and the increase in intracellular production of nitric oxide. An inhibitor of cGMP-dependent protein kinase (PKG), KT5823, suppressed IL-1beta-induced apoptosis, suggesting the involvement of a PKG-dependent pathway in the apoptotic process. One of the major findings in this study is that imidazoline compounds RX871024 and efaroxan, suggested as prototypes of a new generation of drugs against type 2 diabetes, can protect against IL-1beta-induced apoptosis in pancreatic beta-cells, possibly by their inhibition of the expression of iNOS, a key element in the IL-1beta-induced apoptotic pathway in pancreatic beta-cells. These data suggest that imidazoline compounds should be explored as a potential therapeutic agent for the treatment of both type 1 and type 2 diabetes.

Topics: Animals; Apoptosis; Benzofurans; Calcineurin; Calcineurin Inhibitors; Calcium Channel Blockers; Calcium Channels; Cells, Cultured; Dose-Response Relationship, Drug; Enzyme Inhibitors; Gallopamil; Imidazoles; Indoles; Interleukin-1; Islets of Langerhans; Membrane Potentials; Mice; Mice, Obese; Models, Biological; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitriles; Patch-Clamp Techniques; Pyrethrins