title: Voltage-dependent K(+) channels are positive regulators of alpha cell action potential generation and glucagon secretion in mice and humans.
abstract: OBJECTIVE
  The regulation of glucagon secretion from alpha cells is poorly understood. Since action potential firing at low glucose is required for glucagon secretion, we hypothesised that voltage-dependent K(+) (Kv) currents limit glucagon secretion under these conditions, similarly to their role in insulin secretion.
  
  
  METHODS
  Kv currents and action potential firing of mouse and human alpha cells, identified by immunostaining, were examined by whole-cell patch-clamp. Glucagon secretion from mouse and human islets was measured by ELISA.
  
  
  RESULTS
  Kv current density was 35% larger in alpha than in beta cells. Alpha cell Kv channels were sensitive to block by tetraethylammonium (TEA) and 4-aminopyridine. Surprisingly, Kv channel inhibition reduced glucagon release to the same extent as glucose. Robust action potential firing was observed in beta cells when ATP-sensitive K(+) channels were closed, but in alpha cells a negative current (-8 pA) injection was required for action potential firing. TEA (0.5 mmol/l) impaired alpha cell action potential firing, which could be restored by further hyperpolarising current injection (-16 pA). Kv currents were more sensitive to the Kv2 inhibitor stromatoxin (100 nmol/l) in mouse (80%) than in human (45%) alpha cells. Finally, the maxi-K (BK) channel inhibitor iberiotoxin (100 nmol/l) blocked 55% of the current in human alpha cells and inhibited glucagon release from human islets.
  
  
  CONCLUSIONS
  Kv currents in alpha cells are positive regulators of glucagon secretion. These currents, mediated by Kv2 and BK channels, limit membrane depolarisation, and prevent inactivation of alpha cell action potentials and suppression of glucagon release.
authors.affiliation: Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada.
authors.forename: A F
authors.initials: AF
authors.lastname: Spigelman
authors.forename: X
authors.initials: X
authors.lastname: Dai
authors.forename: P E
authors.initials: PE
authors.lastname: MacDonald
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D004594:Electrophysiology; D004797:Enzyme-Linked Immunosorbent Assay; D005934:Glucagon / Q000378:metabolism*; D050416:Glucagon-Secreting Cells / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019789:Tetraethylammonium / Q000494:pharmacology
chemical_list: D024642:Potassium Channels, Voltage-Gated; D019789:Tetraethylammonium; D005934:Glucagon; D015761:4-Aminopyridine
references.citation: J Physiol. 2005 Aug 15;567(Pt 1):159-75
references.pmid: 15932888
references.citation: Diabetes. 2004 Dec;53 Suppl 3:S181-9
references.pmid: 15561909
references.citation: Diabetes. 2004 Mar;53(3):597-607
references.pmid: 14988243
references.citation: J Physiol. 2000 Nov 1;528(Pt 3):497-507
references.pmid: 11060127
references.citation: Endocr Rev. 2007 Feb;28(1):84-116
references.pmid: 17261637
references.citation: J Physiol. 2000 Nov 1;528(Pt 3):509-20
references.pmid: 11060128
references.citation: Diabetes. 2008 Jun;57(6):1618-28
references.pmid: 18390794
references.citation: PLoS Biol. 2007 Jun;5(6):e143
references.pmid: 17503968
references.citation: Endocrinology. 2006 Oct;147(10):4655-63
references.pmid: 16857746
references.citation: Endocrinology. 2007 May;148(5):2157-67
references.pmid: 17303668
references.citation: Pharmacol Rev. 2005 Dec;57(4):473-508
references.pmid: 16382104
references.citation: Mol Endocrinol. 2001 Aug;15(8):1423-35
references.pmid: 11463864
references.citation: Endocrinology. 2005 Nov;146(11):4861-70
references.pmid: 16081632
references.citation: J Physiol. 1970 Sep;210(2):255-64
references.pmid: 5501259
references.citation: J Biol Chem. 1996 Dec 13;271(50):32241-6
references.pmid: 8943282
references.citation: J Biol Chem. 2009 Oct 30;284(44):30441-52
references.pmid: 19690348
references.citation: Cell Metab. 2007 Sep;6(3):229-35
references.pmid: 17767909
references.citation: Endocrinology. 2005 Nov;146(11):4766-75
references.pmid: 16109783
references.citation: Endocr Rev. 2007 May;28(3):253-83
references.pmid: 17409288
references.citation: J Gen Physiol. 1988 Feb;91(2):223-42
references.pmid: 2453603
references.citation: Diabetes. 2009 Feb;58(2):412-21
references.pmid: 19008345
references.citation: Diabetes. 2000 Sep;49(9):1500-10
references.pmid: 10969834
references.citation: J Biol Chem. 2002 Nov 22;277(47):44938-45
references.pmid: 12270920
references.citation: Diabetologia. 2003 Aug;46(8):1046-62
references.pmid: 12830383