Imidazoline NNC77-0074 stimulates insulin secretion and inhibits glucagon release by control of Ca(2+)-dependent exocytosis in pancreatic alpha- and beta-cells.
We have investigated the effects of the novel imidazoline compound (+)-2-(2-(4,5-dihydro-1H-imidazol-2-yl)-thiopene-2-yl-ethyl)-pyridine (NNC77-0074) on stimulus-secretion coupling in isolated pancreatic alpha- and beta-cells. NNC77-0074 stimulated glucose-dependent insulin secretion in intact mouse pancreatic islets. No effect was observed at </=2.5 mM glucose and maximal stimulation occurred at 10-15 mM glucose. NNC77-0074 produced a concentration-dependent stimulation of insulin secretion. Half-maximal (EC(50)) stimulation was observed at 24 microM and at maximally stimulatory concentrations insulin release was doubled. The stimulatory action of NNC77-0074 on insulin secretion was not associated with membrane depolarisation or a change in the activity of ATP-sensitive K(+) channels. Using capacitance measurements, we found that NNC77-0074 stimulated depolarisation-induced exocytosis 2.6-fold without affecting the whole-cell Ca(2+) current when applied via the extracellular medium. The concentration dependence of the stimulatory action was determined by intracellular application of NNC77-0074 through the recording pipette. NNC77-0074 stimulated exocytosis half-maximal at 44 nM and at maximally stimulatory concentrations the rate of exocytosis was increased twofold. NNC77-0074 stimulated depolarised-induced insulin secretion from islets exposed to diazoxide and high external KCl (EC(50)=0.45 microM). The stimulatory action of NNC77-0074 was dependent on protein kinase C activity. NNC77-0074 potently inhibited glucagon secretion from rat islets (EC(50)=11 nM). This was not associated with a change in spontaneous electrical activity and ATP-sensitive K(+) channel activity but resulted from a reduction of the rate of Ca(2+)-dependent exocytosis in single rat alpha-cells (EC(50)=9 nM). Inhibition of exocytosis by NNC77-0074 was pertussis toxin-sensitive and mediated by activation of the protein phosphatase calcineurin. In rat somatotrophs, PC12 cells and mouse cortical neurons NNC77-0074 did not stimulate Ca(2+)-evoked exocytosis, whereas the other imidazoline compounds phentolamine and efaroxan produced 2.5-fold stimulation of exocytosis. Our data suggest that the imidazoline compound NNC77-0074 constitutes a novel class of antidiabetic compounds that stimulates glucose-dependent insulin release while inhibiting glucagon secretion. These actions are exclusively exerted by modulation of exocytosis of the insulin- and glucagon-containing granules.
Høy
Marianne
M
Novo Nordisk A/S, Novo Alle, DK-2880, Bagsvaerd, Denmark.
Olsen
Hervør L
HL
Andersen
Henrik S
HS
Bokvist
Krister
K
Buschard
Karsten
K
Hansen
John
J
Jacobsen
Palle
P
Petersen
Jacob S
JS
Rorsman
Patrik
P
Gromada
Jesper
J
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005089:Exocytosis; D005260:Female; D005934:Glucagon / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology*
C474118:2-(2-(4,5-dihydro-1H-imidazol-2-yl)thiophene-2-ylethyl)pyridine; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007328:Insulin; D015221:Potassium Channels; D011725:Pyridines; D005934:Glucagon; D000242:Cyclic AMP; D011493:Protein Kinase C; D005947:Glucose; D002118:Calcium