title: Early opening of sarcolemmal ATP-sensitive potassium channels is not a key step in PKC-mediated cardioprotection.
abstract: ATP-sensitive potassium (KATP) channels are abundantly expressed in the myocardium. Although a definitive role for the channel remains elusive they have been implicated in the phenomenon of cardioprotection, but the precise mechanism is unclear. We set out to test the hypothesis that the channel protects by opening early during ischemia to shorten action potential duration and reduce electrical excitability thus sparing intracellular ATP. This could reduce reperfusion injury by improving calcium homeostasis. Using a combination of contractile function analysis, calcium fluorescence imaging and patch clamp electrophysiology in cardiomyocytes isolated from adult male Wistar rats, we demonstrated that the opening of sarcolemmal KATP channels was markedly delayed after cardioprotective treatments: ischemic preconditioning, adenosine and PMA. This was due to the preservation of intracellular ATP for longer during simulated ischemia therefore maintaining sarcolemmal KATP channels in the closed state for longer. As the simulated ischemia progressed, KATP channels opened to cause contractile, calcium transient and action potential failure; however there was no indication of any channel activity early during simulated ischemia to impart an energy sparing hyperpolarization or action potential shortening. We present compelling evidence to demonstrate that an early opening of sarcolemmal KATP channels during simulated ischemia is not part of the protective mechanism imparted by ischemic preconditioning or other PKC-dependent cardioprotective stimuli. On the contrary, channel opening was actually delayed. We conclude that sarcolemmal KATP channel opening is a consequence of ATP depletion, not a primary mechanism of ATP preservation in these cells.
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Clinical Sciences Wing, Glenfield General Hospital, Leicester, LE3 9QP, UK.
authors.forename: Sean
authors.initials: S
authors.lastname: Brennan
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Clinical Sciences Wing, Glenfield General Hospital, Leicester, LE3 9QP, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Jackson
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Clinical Sciences Wing, Glenfield General Hospital, Leicester, LE3 9QP, UK.
authors.forename: Manish
authors.initials: M
authors.lastname: Patel
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Clinical Sciences Wing, Glenfield General Hospital, Leicester, LE3 9QP, UK.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Sims
authors.affiliation: Department of Medical and Social Care Education, Maurice Shock Medical Sciences Building, University of Leicester, Leicester, LE1 9HN, UK.
authors.forename: Diane
authors.initials: D
authors.lastname: Hudman
authors.affiliation: Department of Medical and Social Care Education, Maurice Shock Medical Sciences Building, University of Leicester, Leicester, LE1 9HN, UK.
authors.forename: Robert I
authors.initials: RI
authors.lastname: Norman
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Clinical Sciences Wing, Glenfield General Hospital, Leicester, LE3 9QP, UK.
authors.forename: David
authors.initials: D
authors.lastname: Lodwick
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Clinical Sciences Wing, Glenfield General Hospital, Leicester, LE3 9QP, UK. Electronic address: rdr8@le.ac.uk.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Rainbow
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D002316:Cardiotonic Agents / Q000378:metabolism*; D002469:Cell Separation; D003981:Diazoxide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006333:Heart Failure / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology; D015640:Ion Channel Gating / Q000187:drug effects; D019157:Ischemic Preconditioning, Myocardial; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D054086:KATP Channels / Q000378:metabolism*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D015425:Myocardial Reperfusion; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010641:Phenotype; D020110:Pinacidil / Q000494:pharmacology; D051744:Protein Kinase C-epsilon / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017208:Rats, Wistar; D012508:Sarcolemma / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002316:Cardiotonic Agents; D007527:Isoenzymes; D054086:KATP Channels; D047428:Protein Kinase Inhibitors; D020110:Pinacidil; D051744:Protein Kinase C-epsilon; D000241:Adenosine; D013755:Tetradecanoylphorbol Acetate; D003981:Diazoxide
keywords: ATP-sensitive potassium (K(ATP)) channels; Cardioprotection; Ischemic preconditioning; Protein kinase C (PKC)