title: Prolonged oxidative stress inverts the cardiac force-frequency relation: role of altered calcium handling and myofilament calcium responsiveness.
abstract: The normally positive force- and Ca2+ -frequency responses (FFR and CaFR) are inverted in heart failure (HF); whether oxidative stress contributes to these abnormalities is unknown. We evaluated the impact of acute and prolonged oxidative stress on contraction and Ca2+ handling in adult rat cardiomyocytes. Acute (30 min) exposure to H2O2 (100 microM) induced a twofold increase (P<0.025) in intracellular oxyradicals together with contractile depression despite preservation of the Ca2+ transient and the FFR and CaFR to 3 Hz, indicating reduced myofilament Ca2+ responsiveness. In contrast, prolonged (24 h) exposure to the copper-zinc superoxide dismutase inhibitor diethyldithiocarbamic acid (DDC, 1 microM) similarly augmented oxyradicals but also increased cell size, and contraction and Ca2+ transient duration (P<0.025). DDC-treated myocytes displayed inverted FFRs and attenuated (though still positive) CaFRs as compared to control, indicating reduced myofilament Ca2+ responsiveness coupled with altered Ca2+ handling. Protein levels of the Na+ -Ca2+ exchanger (NCX), sarcoplasmic reticular (SR) Ca2+ ATPase (SERCA2), and serine-16 phosphorylated phospholamban (pSer16-PLB) were increased (P<0.025), whereas dihydropyridine receptor abundance was decreased. Total PLB and ryanodine receptor protein expression were unchanged. Caffeine-induced Ca2+ release showed increased NCX activity (P<0.025) without changes in total releasable SR Ca2+, suggesting compensatory changes in SERCA2 and pSer16-PLB to maintain SR Ca2+ load. The superoxide scavenger Tiron attenuated these effects. Thus, acute oxyradical exposure rapidly depresses myofibrillar Ca2+ responsiveness. Prolonged oxidative stress further induces alterations in Ca2+ handling that combined with extant reductions in myofibrillar responsiveness invert the FFR. With regard to Ca2+ handling, reduced transsarcolemmal Ca2+ flux rather than reduced SR Ca2+ uptake was the primary determinant of a negative FFR. Analogous changes may be operative in HF, a state characterized by both oxidative stress and Ca2+ dysregulation.
authors.affiliation: Institute of Molecular Cardiology, Department of Medicine, University of Louisville Health Sciences Center, University of Louisville, ACB, 3rd Floor, 550 South Jackson Street, Louisville, KY 40202, USA.
authors.forename: Jianzhu
authors.initials: J
authors.lastname: Luo
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Xuan
authors.forename: Yan
authors.initials: Y
authors.lastname: Gu
authors.forename: Sumanth D
authors.initials: SD
authors.lastname: Prabhu
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004050:Ditiocarb / Q000494:pharmacology; D006333:Heart Failure / Q000378:metabolism / Q000473:pathology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018384:Oxidative Stress; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D004050:Ditiocarb; D006861:Hydrogen Peroxide; D017382:Reactive Oxygen Species; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger; D013482:Superoxide Dismutase; D000099211:Phospholamban; C506948:Atp2a2 protein, rat