title: Disruption of pancreatic beta-cell lipid rafts modifies Kv2.1 channel gating and insulin exocytosis.
abstract: In pancreatic beta-cells, the predominant voltage-gated Ca(2+) channel (Ca(V)1.2) and K(+) channel (K(V)2.1) are directly coupled to SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor) proteins. These SNARE proteins modulate channel expression and gating and closely associate these channels with the insulin secretory vesicles. We show that K(V)2.1 and Ca(V)1.2, but not K(V)1.4, SUR1, or Kir6.2, target to specialized cholesterol-rich lipid raft domains on beta-cell plasma membranes. Similarly, the SNARE proteins syntaxin 1A, SNAP-25, and VAMP-2, but not Munc-13-1 or n-Sec1, are associated with lipid rafts. Disruption of the lipid rafts by depleting membrane cholesterol with methyl-beta-cyclodextrin shunts K(V)2.1, Ca(V)1.2, and SNARE proteins out of lipid rafts. Furthermore, methyl-beta-cyclodextrin inhibits K(V)2.1 but not Ca(V)1.2 channel activity and enhances single-cell exocytic events and insulin secretion. Membrane compartmentalization of ion channels and SNARE proteins in lipid rafts may be critical for the temporal and spatial coordination of insulin release, forming what has been described as the excitosome complex.
authors.affiliation: Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8,Canada.
authors.forename: Fuzhen
authors.initials: F
authors.lastname: Xia
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Gao
authors.forename: Edwin
authors.initials: E
authors.lastname: Kwan
authors.forename: Patrick P L
authors.initials: PP
authors.lastname: Lam
authors.forename: Lillian
authors.initials: L
authors.lastname: Chan
authors.forename: Keiyan
authors.initials: K
authors.lastname: Sy
authors.forename: Laura
authors.initials: L
authors.lastname: Sheu
authors.forename: Michael B
authors.initials: MB
authors.lastname: Wheeler
authors.forename: Herbert Y
authors.initials: HY
authors.lastname: Gaisano
authors.forename: Robert G
authors.initials: RG
authors.lastname: Tsushima
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D006224:Cricetinae; D003505:Cyclodextrins / Q000737:chemistry; D051668:Delayed Rectifier Potassium Channels; D004594:Electrophysiology; D005089:Exocytosis; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007477:Ions; D007515:Islets of Langerhans / Q000378:metabolism*; D021962:Membrane Microdomains / Q000737:chemistry*; D008565:Membrane Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry*; D024642:Potassium Channels, Voltage-Gated; D017434:Protein Structure, Tertiary; D051381:Rats; D050600:SNARE Proteins; D051669:Shab Potassium Channels; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D047392:beta-Cyclodextrins
chemical_list: D003505:Cyclodextrins; D051668:Delayed Rectifier Potassium Channels; D007328:Insulin; D007477:Ions; C496991:Kcnb1 protein, rat; D008565:Membrane Proteins; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D050600:SNARE Proteins; D051669:Shab Potassium Channels; C494213:Stx1a protein, rat; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D011188:Potassium