Augmented protein kinase C-α-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 PKC-alpha may be of particular importance. Here, we examined PKC-alpha quantity, 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 PKC-alpha expression 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-[Ca2+] relation to obtain Ca2+-saturated maximal force (F-max) and myofilament Ca2+ sensitivity ( indexed by EC50) before and after incubation with PKC-alpha, protein phosphatase type 1 (PP1), or PP2a. PKC-alpha treatment 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 (approximate to 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-alpha. 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-alpha.