Aims: The region-specific mechanical function of left ventricular (LV) murinecardiomyocytes and the role of phosphorylation and oxidative modifications of myofilamentproteins were investigated in the process of post-myocardial infarction (MI) remodeling 10weeks after ligation of the left anterior descending (LAD) coronary artery. Methods andResults: Permeabilized murine cardiomyocytes from the remaining anterior and a remotenoninfarcted inferior LV area were compared with those of noninfarcted age-matchedcontrols. Myofilament phosphorylation, sulfhydryl (SH) oxidation and carbonylation werealso assayed. The Ca2+ sensitivity of force production was significantly lower in the anteriorwall (pCa50:5.81?0.03, mean?SEM, at 2.3 ?m sarcomere length) than that in the controls(pCa50:5.91?0.02) or in the MI inferior area (pCa50:5.88?0.02). The level of troponin Iphosphorylation was lower and that of myofilament protein SH oxidation was higher in theanterior location relative to controls, but these changes did not explain the differences in Ca2+sensitivities. On the other hand, significantly higher carbonylation levels [e.g. in myosinheavy chain (MHC) and actin] were observed in the MI anterior wall [carbonylation index(CI), CIMHC:2.06?0.46, CIactin:1.46?0.18] than in the controls (CI:1). In vitro Fenton-basedmyofilament carbonylation in the control cardiomyocytes also decreased the Ca2+ sensitivityof force production irrespective of the phosphorylation status of the myofilaments.Furthermore, the Ca2+ sensitivity correlated strongly with myofilament carbonylation levels inall investigated samples. Conclusions: Post-MI myocardial remodeling involves increasedmyofibrillar protein carbonylation and decreased Ca2+ sensitivity of force production, leadingpotentially to contractile dysfunction in the remaining cardiomyocytes of the infarcted area