title: Regulation of the Na+/Ca2+ exchanger by pyridine nucleotide redox potential in ventricular myocytes.
abstract: The cardiac Na(+)/Ca(2+) exchanger (NCX) is the major Ca(2+) efflux pathway on the sarcolemma, counterbalancing Ca(2+) influx via L-type Ca(2+) current during excitation-contraction coupling. Altered NCX activity modulates the sarcoplastic reticulum Ca(2+) load and can contribute to abnormal Ca(2+) handling and arrhythmias. NADH/NAD(+) is the main redox couple controlling mitochondrial energy production, glycolysis, and other redox reactions. Here, we tested whether cytosolic NADH/NAD(+) redox potential regulates NCX activity in adult cardiomyocytes. NCX current (INCX), measured with whole cell patch clamp, was inhibited in response to cytosolic NADH loaded directly via pipette or increased by extracellular lactate perfusion, whereas an increase of mitochondrial NADH had no effect. Reactive oxygen species (ROS) accumulation was enhanced by increasing cytosolic NADH, and NADH-induced INCX inhibition was abolished by the H2O2 scavenger catalase. NADH-induced ROS accumulation was independent of mitochondrial respiration (rotenone-insensitive) but was inhibited by the flavoenzyme blocker diphenylene iodonium. NADPH oxidase was ruled out as the effector because INCX was insensitive to cytosolic NADPH, and NADH-induced ROS and INCX inhibition were not abrogated by the specific NADPH oxidase inhibitor gp91ds-tat. This study reveals a novel mechanism of NCX regulation by cytosolic NADH/NAD(+) redox potential through a ROS-generating NADH-driven flavoprotein oxidase. The mechanism is likely to play a key role in Ca(2+) homeostasis and the response to alterations in the cytosolic pyridine nucleotide redox state during ischemia-reperfusion or other cardiovascular diseases.
authors.affiliation: From the Division of Cardiology, Department of Medicine, The Johns Hopkins University, Baltimore, Maryland 21205.
authors.forename: Ting
authors.initials: T
authors.lastname: Liu
authors.forename: Brian
authors.initials: B
authors.lastname: O'Rourke
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006023:Glycoproteins / Q000494:pharmacology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000378:metabolism* / Q000473:pathology; D006706:Homeostasis / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000378:metabolism; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D009243:NAD / Q000378:metabolism*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D006023:Glycoproteins; D009861:Onium Compounds; D019831:Sodium-Calcium Exchanger; C473031:gp91ds-tat protein, chimeric; D009243:NAD; C007517:diphenyleneiodonium; D006861:Hydrogen Peroxide; D002374:Catalase; D019255:NADPH Oxidases; D002118:Calcium
keywords: Excitation-Contraction Coupling; Ischemia; Metabolism; NADH; Reactive Oxygen Species (ROS); Sodium Calcium Exchange
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