title: Characterisation of new KATP-channel mutations associated with congenital hyperinsulinism in the Finnish population.
abstract: OBJECTIVE
  ATP-sensitive potassium (K(ATP)) channels are crucial for the regulation of insulin secretion from pancreatic beta cells and mutations in either the Kir6.2 or SUR1 subunit of this channel can cause congenital hyperinsulinism (CHI). The aim of this study was to analyse the functional consequences of four CHI mutations (A1457T, V1550D and L1551V in SUR1, and K67N in Kir6.2) recently identified in the Finnish population.
  
  
  METHODS
  Wild type or mutant Kir6.2 and SUR1 subunits were coexpressed in Xenopus oocytes. The functional properties of the channels were examined by measuring currents in intact oocytes or giant inside-out membrane patches. Surface expression was measured by enzyme-linked immunosorbance assay, using HA-epitope-tagged subunits.
  
  
  RESULTS
  Two mutations (A1457T and V1550D) prevented trafficking of the channel to the plasma membrane. The L1551V mutation reduced surface expression 40-fold, and caused loss of MgADP and diazoxide activation. Both these factors will contribute to the lack of K(ATP) current activation observed in response to metabolic inhibition in intact oocytes. The L1551V mutation also increased the channel open probability, thereby producing a reduction in ATP-sensitivity (from 10 micro mol/l to 120 micro mol/l). The fourth mutation (K67N mutation in Kir6.2) did not affect surface expression nor alter the properties of K(ATP) channels in excised patches, but resulted in a reduced K(ATP) current amplitude in intact cells on metabolic inhibition, through an unidentified mechanism.
  
  
  CONCLUSIONS
  The four CHI mutations disrupted K(ATP) channel activity by different mechanisms. Our results are discussed in relation to the CHI phenotype observed in patients with these mutations.
authors.affiliation: Department of Clinical Biochemistry, University of Cambridge, UK.
authors.forename: F
authors.initials: F
authors.lastname: Reimann
authors.forename: H
authors.initials: H
authors.lastname: Huopio
authors.forename: M
authors.initials: M
authors.lastname: Dabrowski
authors.forename: P
authors.initials: P
authors.lastname: Proks
authors.forename: F M
authors.initials: FM
authors.lastname: Gribble
authors.forename: M
authors.initials: M
authors.lastname: Laakso
authors.forename: T
authors.initials: T
authors.lastname: Otonkoski
authors.forename: F M
authors.initials: FM
authors.lastname: Ashcroft
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004553:Electric Conductivity; D005260:Female; D005387:Finland; D006801:Humans; D006946:Hyperinsulinism / Q000151:congenital* / Q000235:genetics*; D009154:Mutation; D009865:Oocytes; D015221:Potassium Channels / Q000235:genetics* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000502:physiology; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D014982:Xenopus laevis
chemical_list: C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors