کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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2192560 | 1097903 | 2006 | 12 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Prolonged oxidative stress inverts the cardiac force–frequency relation: role of altered calcium handling and myofilament calcium responsiveness Prolonged oxidative stress inverts the cardiac force–frequency relation: role of altered calcium handling and myofilament calcium responsiveness](/preview/png/2192560.png)
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 μM) 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 μM) 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.
Journal: Journal of Molecular and Cellular Cardiology - Volume 40, Issue 1, January 2006, Pages 64–75