Phentolamine inhibits exocytosis of glucagon by Gi2 protein-dependent activation of calcineurin in rat pancreatic alpha -cells

J Biol Chem. 2001 Jan 12;276(2):924-30. doi: 10.1074/jbc.M007562200.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylate Cyclase Toxin
  • Animals
  • Calcineurin / metabolism*
  • Cells, Cultured
  • Clorgyline / pharmacology
  • Cyclosporine / pharmacology
  • Cystamine / analogs & derivatives*
  • Cystamine / pharmacology
  • Diazoxide / pharmacology
  • Exocytosis / drug effects*
  • GTP-Binding Protein alpha Subunit, Gi2
  • GTP-Binding Protein alpha Subunits, Gi-Go / antagonists & inhibitors
  • GTP-Binding Protein alpha Subunits, Gi-Go / genetics
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism*
  • Glucagon / metabolism*
  • Imidazoles / pharmacology
  • Indoles / pharmacology
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / physiology*
  • Male
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Nitriles
  • Oligodeoxyribonucleotides, Antisense / pharmacology*
  • Pertussis Toxin
  • Phentolamine / pharmacology*
  • Potassium Channels / drug effects
  • Potassium Channels / physiology*
  • Proto-Oncogene Proteins / antagonists & inhibitors
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Pyrethrins / pharmacology
  • Rats
  • Rats, Inbred Lew
  • Virulence Factors, Bordetella / pharmacology

Substances

  • 2-(2-imidazolin-2-yl)-1-phenyl-1H-indole
  • Adenylate Cyclase Toxin
  • Imidazoles
  • Indoles
  • Nitriles
  • Oligodeoxyribonucleotides, Antisense
  • Potassium Channels
  • Proto-Oncogene Proteins
  • Pyrethrins
  • Virulence Factors, Bordetella
  • decamethrin
  • benextramine
  • Cyclosporine
  • Glucagon
  • Pertussis Toxin
  • Calcineurin
  • GTP-Binding Protein alpha Subunit, Gi2
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • Gnai2 protein, rat
  • Clorgyline
  • Diazoxide
  • Cystamine
  • Phentolamine