title: Upregulation of basolateral small conductance potassium channels (KCNQ1/KCNE3) in ulcerative colitis.
abstract: BACKGROUND
  Basolateral K(+) channels hyperpolarize colonocytes to ensure Na(+) (and thus water) absorption. Small conductance basolateral (KCNQ1/KCNE3) K(+) channels have never been evaluated in human colon. We therefore evaluated KCNQ1/KCNE3 channels in distal colonic crypts obtained from normal and active ulcerative colitis (UC) patients.
  
  
  METHODS
  KCNQ1 and KCNE3 mRNA levels were determined by qPCR, and KCNQ1/KCNE3 channel activity in normal and UC crypts, and the effects of forskolin (activator of adenylate cyclase) and UC-related proinflammatory cytokines on normal crypts, studied by patch clamp recording.
  
  
  RESULTS
  Whereas KCNQ1 and KCNE3 mRNA expression was similar in normal and UC crypts, single 6.8 pS channels were seen in 36% of basolateral patches in normal crypts, and to an even greater extent (74% of patches, P < 0.001) in UC crypts, with two or more channels per patch. Channel activity was 10-fold higher (P < 0.001) in UC crypts, with a greater contribution to basolateral conductance (5.85 ± 0.62 mS cm(-2)) than in controls (0.28 ± 0.04 mS cm(-2), P < 0.001). In control crypts, forskolin and thromboxane A2 stimulated channel activity 30-fold and 10-fold respectively, while PGE2, IL-1β, and LTD4 had no effect.
  
  
  CONCLUSIONS
  KCNQ1/KCNE3 channels make only a small contribution to basolateral conductance in normal colonic crypts, with increased channel activity in UC appearing insufficient to prevent colonic cell depolarization in this disease. This supports the proposal that defective Na(+) absorption rather than enhanced Cl(-) secretion, is the dominant pathophysiological mechanism of diarrhea in UC.
authors.affiliation: Institute of Membrane and Systems Biology, University of Leeds, UK.
authors.forename: Adel
authors.initials: A
authors.lastname: Al-Hazza
authors.affiliation: Institute of Membrane and Systems Biology, University of Leeds, UK.
authors.forename: John
authors.initials: J
authors.lastname: Linley
authors.affiliation: Institute of Membrane and Systems Biology, University of Leeds, UK.
authors.forename: Qadeer
authors.initials: Q
authors.lastname: Aziz
authors.affiliation: Institute of Membrane and Systems Biology, University of Leeds, UK.
authors.forename: Malcolm
authors.initials: M
authors.lastname: Hunter
authors.affiliation: Leeds Institute of Biomedical and Clinical Sciences, St. James's University Hospital, Leeds, UK. Electronic address: g.i.sandle@leeds.ac.uk.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Sandle
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003093:Colitis, Ulcerative / Q000378:metabolism*; D003106:Colon / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D015640:Ion Channel Gating; D051657:KCNQ1 Potassium Channel / Q000378:metabolism*; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C418492:KCNE3 protein, human; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D024642:Potassium Channels, Voltage-Gated; D011188:Potassium
keywords: Human colonic crypts; KCNQ1/KCNE3 channels; Patch clamp; Ulcerative colitis