Left ventricular myofilament dysfunction in rat experimental hypertrophy and congestive heart failure

Center for Cardiovascular Research, 1 Department of Physiology and Biophysics, Department of Medicine; and 2 Section of Cardiology, University of Illinois, Chicago, Illinois Submitted 26 May 2006 ; accepted in final form 28 June 2006 It is currently unclear whether left ventricular (LV) myofilament function is depressed in experimental LV hypertrophy (LVH) or congestive heart failure (CHF). To address this issue, we studied pressure overload-induced LV hypertrophy (POLVH) and myocardial infarction-elicited congestive heart failure (MICHF) in rats. LV myocytes were isolated from control, POLVH, and MICHF hearts by mechanical homogenization, skinned with Triton, and attached to micropipettes that projected from a sensitive force transducer and high-speed motor. A subset of cells was treated with either unphosphorylated, recombinant cardiac troponin (cTn) or cTn purified from either control or failing ventricles. LV myofilament function was characterized by the force-[Ca 2+ ] relation yielding Ca 2+ -saturated maximal force (F max ), myofilament Ca 2+ sensitivity (EC 50 ), and cooperativity (Hill coefficient, n H ) parameters. POLVH was associated with a 35% reduction in F max and 36% increase in EC 50 . Similarly, MICHF resulted in a 42% reduction in F max and a 30% increase in EC 50 . Incorporation of recombinant cTn or purified control cTn into failing cells restored myofilament Ca 2+ sensitivity toward levels observed in control cells. In contrast, integration of cTn purified from failing ventricles into control myocytes increased EC 50 to levels observed in failing myocytes. The F max parameter was not markedly affected by troponin exchange. cTnI phosphorylation was increased in both POLVH and MICHF left ventricles. We conclude that depressed myofilament Ca 2+ sensitivity in experimental LVH and CHF is due, in part, to a decreased functional role of cTn that likely involves augmented phosphorylation of cTnI. left ventricle; troponin; phosphorylation; cardiac disease Address for reprint requests and other correspondence: P. P. de Tombe, Dept. of Physiology & Biophysics, Univ. of Illinois at Chicago, 835 S. Wolcott (M/C 901), Chicago, IL 60612 (email: pdetombe{at}uic.edu )