title: Expression and function of Kv7.4 channels in rat cardiac mitochondria: possible targets for cardioprotection.
abstract: OBJECTIVE
  Plasmalemmal Kv7.1 (KCNQ1) channels are critical players in cardiac excitability; however, little is known on the functional role of additional Kv7 family members (Kv7.2-5) in cardiac cells. In this work, the expression, function, cellular and subcellular localization, and potential cardioprotective role against anoxic-ischaemic cardiac injury of Kv7.4 channels have been investigated.
  
  
  RESULTS
  Expression of Kv7.1 and Kv7.4 transcripts was found in rat heart tissue by quantitative polymerase chain reaction. Western blots detected Kv7.4 subunits in mitochondria from Kv7.4-transfected cells, H9c2 cardiomyoblasts, freshly isolated adult cardiomyocytes, and whole hearts. Immunofluorescence experiments revealed that Kv7.4 subunits co-localized with mitochondrial markers in cardiac cells, with ∼ 30-40% of cardiac mitochondria being labelled by Kv7.4 antibodies, a result also confirmed by immunogold electron microscopy experiments. In isolated cardiac (but not liver) mitochondria, retigabine (1-30 µM) and flupirtine (30 µM), two selective Kv7 activators, increased Tl(+) influx, depolarized the membrane potential, and inhibited calcium uptake; all these effects were antagonized by the Kv7 blocker XE991. In intact H9c2 cells, reducing Kv7.4 expression by RNA interference blunted retigabine-induced mitochondrial membrane depolarization; in these cells, retigabine decreased mitochondrial Ca(2+) levels and increased radical oxygen species production, both effects prevented by XE991. Finally, retigabine reduced cellular damage in H9c2 cells exposed to anoxia/re-oxygenation and largely prevented the functional and morphological changes triggered by global ischaemia/reperfusion (I/R) in Langendorff-perfused rat hearts.
  
  
  CONCLUSIONS
  Kv7.4 channels are present and functional in cardiac mitochondria; their activation exerts a significant cardioprotective role, making them potential therapeutic targets against I/R-induced cardiac injury.
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Lara
authors.initials: L
authors.lastname: Testai
authors.affiliation: Department of Neuroscience, Division of Pharmacology, University of Naples 'Federico II', Naples, Italy Vascular Biology Research Centre, Institute of Cardiovascular and Cell Sciences, St George's University of London, London, UK.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Barrese
authors.affiliation: Department of Medicine and Health Science "Vincenzo Tiberio", University of Molise, Campobasso, Italy.
authors.forename: Maria Virginia
authors.initials: MV
authors.lastname: Soldovieri
authors.affiliation: Department of Medicine and Health Science "Vincenzo Tiberio", University of Molise, Campobasso, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ambrosino
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Alma
authors.initials: A
authors.lastname: Martelli
authors.affiliation: Department of Medicine and Health Science "Vincenzo Tiberio", University of Molise, Campobasso, Italy.
authors.forename: Iolanda
authors.initials: I
authors.lastname: Vinciguerra
authors.affiliation: Department of Neuroscience, Division of Pharmacology, University of Naples 'Federico II', Naples, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Miceli
authors.affiliation: Vascular Biology Research Centre, Institute of Cardiovascular and Cell Sciences, St George's University of London, London, UK.
authors.forename: Iain Andrew
authors.initials: IA
authors.lastname: Greenwood
authors.affiliation: Cardiovascular Division, Faculty of Life Sciences and Medicine, King's College London, London, UK.
authors.forename: Michael John
authors.initials: MJ
authors.lastname: Curtis
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Breschi
authors.affiliation: Department of Neuroscience, Division of Pharmacology, University of Naples 'Federico II', Naples, Italy.
authors.forename: Maria Josè
authors.initials: MJ
authors.lastname: Sisalli
authors.affiliation: Department of Neuroscience, Division of Pharmacology, University of Naples 'Federico II', Naples, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Scorziello
authors.affiliation: Department of Neurosciences, University of the Basque Country UPV/EHU, Leioa, Spain.
authors.forename: Miren Josune
authors.initials: MJ
authors.lastname: Canduela
authors.affiliation: Department of Neurosciences, University of the Basque Country UPV/EHU, Leioa, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Grandes
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Calderone
authors.affiliation: Department of Neuroscience, Division of Pharmacology, University of Naples 'Federico II', Naples, Italy Department of Medicine and Health Science "Vincenzo Tiberio", University of Molise, Campobasso, Italy m.taglialatela@unimol.it.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Taglialatela
mesh_terms: D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002219:Carbamates / Q000494:pharmacology; D051656:KCNQ Potassium Channels / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010655:Phenylenediamines / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats
chemical_list: D000631:Aminopyridines; D002219:Carbamates; D051656:KCNQ Potassium Channels; C492166:Kcnq4 protein, rat; D010655:Phenylenediamines; D026902:Potassium Channel Blockers; C101866:ezogabine; C034161:flupirtine
keywords: Cardioprotection; Ischaemia–reperfusion cardiac damage; Kv7 potassium channels; Mitochondria; Retigabine