PKC depresses cardiac myocyte power output and limits the phosphorylation and mechanical effects by PKA

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Protein kinase C (PKC) targets and phosphorylates myofibrillar proteins in cardiac myocytes, and PKC activity appears to be up-regulated in failing human hearts (Bowling et al., 1999). Since PKC phosphorylation of myofibrillar proteins affects myocyte contractility, we sought to directly test the effects of PKC phosphorylation of myofilament proteins on myocyte power output. We compared isometric force, loaded shortening velocity, and power output in skinned rat cardiac myocytes before and after treatment with the catalytic subunit of PKC.