Interventricular differences in myofilament function in experimental congestive heart failure

This study was conducted to identify molecular mechanisms which explain interventricular differences in myofilament function in experimental congestive heart failure (CHF). CHF was induced in rats by chronic aortic banding or myocardial infarction for 32-36 weeks. Right and left ventricular (RV, LV) myocytes were mechanically isolated, triton-skinned, and attached to a force transducer and motor arm. Myofilament force-[Ca(2+)] relations assessed maximal Ca(2+)-saturated force (F(max)) and the [Ca(2+)] at 50% of F(max) (EC(50)). Myofilament protein phosphorylation was determined via ProQ diamond phospho-staining. Protein kinase C (PKC)-alpha expression/activation and site-specific phosphorylation of cardiac troponin I (cTnI) and cardiac troponin T (cTnT) were measured via immunoblotting. Relative to controls, failing RV myocytes displayed a similar to 45% decrease in F(max) with no change in EC(50), whereas failing LV myocytes displayed a similar to 45% decrease in Fmax and similar to 50% increase in EC(50). Failing LV myofilaments were less Ca(2+)-sensitive (37% increase in EC(50)) than failing RV myofilaments. Expression and activation of PKC-alpha was increased twofold in failing RV myocardium and relative to the RV, PKC-alpha was twofold higher in the failing LV, while PKC-beta expression was unchanged by CHF. PKC-alpha-dependent phosphorylation and PP1-mediated dephosphorylation of failing RV myofilaments increased EC(50) and increased F(max), respectively. Phosphorylation of cTnI and cTnT was greater in failing LV myofilaments than in failing RV myofilaments. RV myofilament function is depressed in experimental CHF in association with increased PKC-alpha signaling and myofilament protein phosphorylation. Furthermore, myofilament dysfunction is greater in the LV compared to the RV due in part to increased PKC-alpha activation and phosphorylation of cTnI and cTnT.