title: The voltage-dependent potassium channel subunit Kv2.1 regulates insulin secretion from rodent and human islets independently of its electrical function.
abstract: OBJECTIVE
  It is thought that the voltage-dependent potassium channel subunit Kv2.1 (Kv2.1) regulates insulin secretion by controlling beta cell electrical excitability. However, this role of Kv2.1 in human insulin secretion has been questioned. Interestingly, Kv2.1 can also regulate exocytosis through direct interaction of its C-terminus with the soluble NSF attachment receptor (SNARE) protein, syntaxin 1A. We hypothesised that this interaction mediates insulin secretion independently of Kv2.1 electrical function.
  
  
  METHODS
  Wild-type Kv2.1 or mutants lacking electrical function and syntaxin 1A binding were studied in rodent and human beta cells, and in INS-1 cells. Small intracellular fragments of the channel were used to disrupt native Kv2.1-syntaxin 1A complexes. Single-cell exocytosis and ion channel currents were monitored by patch-clamp electrophysiology. Interaction between Kv2.1, syntaxin 1A and other SNARE proteins was probed by immunoprecipitation. Whole-islet Ca(2+)-responses were monitored by ratiometric Fura red fluorescence and insulin secretion was measured.
  
  
  RESULTS
  Upregulation of Kv2.1 directly augmented beta cell exocytosis. This happened independently of channel electrical function, but was dependent on the Kv2.1 C-terminal syntaxin 1A-binding domain. Intracellular fragments of the Kv2.1 C-terminus disrupted native Kv2.1-syntaxin 1A interaction and impaired glucose-stimulated insulin secretion. This was not due to altered ion channel activity or impaired Ca(2+)-responses to glucose, but to reduced SNARE complex formation and Ca(2+)-dependent exocytosis.
  
  
  CONCLUSIONS
  Direct interaction between syntaxin 1A and the Kv2.1 C-terminus is required for efficient insulin exocytosis and glucose-stimulated insulin secretion. This demonstrates that native Kv2.1-syntaxin 1A interaction plays a key role in human insulin secretion, which is separate from the channel's electrical function.
authors.affiliation: Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada T6G 2E1.
authors.forename: X Q
authors.initials: XQ
authors.lastname: Dai
authors.forename: J E
authors.initials: JE
authors.lastname: Manning Fox
authors.forename: D
authors.initials: D
authors.lastname: Chikvashvili
authors.forename: M
authors.initials: M
authors.lastname: Casimir
authors.forename: G
authors.initials: G
authors.lastname: Plummer
authors.forename: C
authors.initials: C
authors.lastname: Hajmrle
authors.forename: A F
authors.initials: AF
authors.lastname: Spigelman
authors.forename: T
authors.initials: T
authors.lastname: Kin
authors.forename: D
authors.initials: D
authors.lastname: Singer-Lahat
authors.forename: Y
authors.initials: Y
authors.lastname: Kang
authors.forename: A M J
authors.initials: AM
authors.lastname: Shapiro
authors.forename: H Y
authors.initials: HY
authors.lastname: Gaisano
authors.forename: I
authors.initials: I
authors.lastname: Lotan
authors.forename: P E
authors.initials: PE
authors.lastname: Macdonald
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004594:Electrophysiology; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D051381:Rats; D051669:Shab Potassium Channels / Q000235:genetics / Q000378:metabolism*; D050827:Syntaxin 1 / Q000378:metabolism
chemical_list: D007328:Insulin; D051669:Shab Potassium Channels; D050827:Syntaxin 1