Phentolamine inhibits exocytosis of glucagon by Gi2 protein-dependent activation of calcineurin in rat pancreatic alpha -cells.
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.
Høy
M
M
Laboratory of Islet Cell Physiology, Novo Nordisk A/S, Novo Alle, DK-2880 Bagsvaerd, Bartholin Instituttet, Kommunehospitalet, Øster Farimagsgade 5, DK-1353 Copenhagen, Denmark.
Bokvist
K
K
Xiao-Gang
W
W
Hansen
J
J
Juhl
K
K
Berggren
P O
PO
Buschard
K
K
Gromada
J
J
D037361:Adenylate Cyclase Toxin; D000818:Animals; D019703:Calcineurin / Q000378:metabolism*; D002478:Cells, Cultured; D003010:Clorgyline / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D003538:Cystamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects*; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005934:Glucagon / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009570:Nitriles; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology*; D037342:Pertussis Toxin; D010646:Phentolamine / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011722:Pyrethrins / Q000494:pharmacology; D051381:Rats; D011917:Rats, Inbred Lew; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
C101943:2-(2-imidazolin-2-yl)-1-phenyl-1H-indole; D037361:Adenylate Cyclase Toxin; D007093:Imidazoles; D007211:Indoles; D009570:Nitriles; D020319:Oligodeoxyribonucleotides, Antisense; D015221:Potassium Channels; D011518:Proto-Oncogene Proteins; D011722:Pyrethrins; D010566:Virulence Factors, Bordetella; C017180:decamethrin; C029998:benextramine; D016572:Cyclosporine; D005934:Glucagon; D037342:Pertussis Toxin; D019703:Calcineurin; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498017:Gnai2 protein, rat; D003010:Clorgyline; D003981:Diazoxide; D003538:Cystamine; D010646:Phentolamine