Augmented Protein Kinase C- –Induced Myofilament Protein Phosphorylation Contributes to Myofilament Dysfunction in Experimental Congestive Heart Failure

It is becoming clear that upregulated protein kinase C (PKC) signaling plays a role in reduced ventricular myofilament contractility observed in congestive heart failure. However, data are scant regarding which PKC isozymes are involved. There is evidence that PKCmay be of particular importance. Here, we examined PKCquantity, activity, and signaling to myofilaments in chronically remodeled myocytes obtained from rats in either early heart failure or end-stage congestive heart failure. Immunoblotting revealed that PKCexpression and activation was unaltered in early heart failure but increased in end-stage congestive heart failure. Left ventricular myocytes were isolated by mechanical homogenization, Triton-skinned, and attached to micropipettes that projected from a force transducer and motor. Myofilament function was characterized by an active force–[Ca ] relation to obtain Ca -saturated maximal force (Fmax) and myofilament Ca 2 sensitivity (indexed by EC50) before and after incubation with PKC, protein phosphatase type 1 (PP1), or PP2a. PKCtreatment induced a 30% decline in Fmax and 55% increase in the EC50 in control cells but had no impact on myofilament function in failing cells. PP1-mediated dephosphorylation increased Fmax (15%) and decreased EC50 ( 20%) in failing myofilaments but had no effect in control cells. PP2a-dependent dephosphorylation had no effect on myofilament function in either group. Lastly, PP1 dephosphorylation restored myofilament function in control cells hyperphosphorylated with PKC. Collectively, our results suggest that in end-stage congestive heart failure, the myofilament proteins exist in a hyperphosphorylated state attributable, in part, to increased activity and signaling of PKC. (Circ Res. 2007;101:195-204.)