title: Downregulation of Kv1.5 K channels by the AMP-activated protein kinase.
abstract: BACKGROUND
  The voltage gated K(+) channel Kv1.5 participates in the repolarization of a wide variety of cell types. Kv1.5 is downregulated during hypoxia, which is known to stimulate the energy-sensing AMP-activated serine/threonine protein kinase (AMPK). AMPK is a powerful regulator of nutrient transport and metabolism. Moreover, AMPK is known to downregulate several ion channels, an effect at least in part due to stimulation of the ubiquitin ligase Nedd4- 2. The present study explored whether AMPK regulates Kv1.5.
  
  
  METHODS
  cRNA encoding Kv1.5 was injected into Xenopus oocytes with and without additional injection of wild-type AMPK (α1 β 1γ1), of constitutively active (γR70Q)AMPK (α1 β 1γ1(R70Q)), of inactive mutant (αK45R)AMPK (α1(K45R)β1γ1), or of Nedd4-2. Kv1.5 activity was determined by two-electrode voltage-clamp. Moreover, Kv1.5 protein abundance in the cell membrane was determined by chemiluminescence and immunostaining with subsequent confocal microscopy.
  
  
  RESULTS
  Coexpression of wild-type AMPK(WT) and constitutively active AMPK(γR70Q), but not of inactive AMPK(αK45R) significantly reduced Kv1.5-mediated currents. Coexpression of constitutively active AMPKγR70Q further reduced Kv1.5 K(+) channel protein abundance in the cell membrane. Co-expression of Nedd4-2 similarly downregulated Kv1.5-mediated currents.
  
  
  CONCLUSIONS
  AMPK is a potent regulator of Kv1.5. AMPK inhibits Kv1.5 presumably in part by activation of Nedd4- 2 with subsequent clearance of channel protein from the cell membrane.
authors.affiliation: Department of Physiology, University of Tübingen, Tübingen, Germany.
authors.forename: Sobuj
authors.initials: S
authors.lastname: Mia
authors.forename: Carlos
authors.initials: C
authors.lastname: Munoz
authors.forename: Tatsiana
authors.initials: T
authors.lastname: Pakladok
authors.forename: Gulab
authors.initials: G
authors.lastname: Siraskar
authors.forename: Jakob
authors.initials: J
authors.lastname: Voelkl
authors.forename: Ioana
authors.initials: I
authors.lastname: Alesutan
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015536:Down-Regulation; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D051666:Kv1.5 Potassium Channel / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D000075702:Nedd4 Ubiquitin Protein Ligases; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D051666:Kv1.5 Potassium Channel; D029867:Xenopus Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618482:Nedd4 protein, Xenopus; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; C000618460:nedd4l protein, Xenopus; D044767:Ubiquitin-Protein Ligases; D055372:AMP-Activated Protein Kinases