Background—Increased expression of Ca²⁺-sensitive protein kinase C (PKC) isoforms may be important markers of heart failure. Our aim was to determine the relative expression of PKC-β1, -β2, and -α in failed and nonfailed myocardium.

Methods and Results—Explanted hearts of patients in whom dilated cardiomyopathy or ischemic cardiomyopathy was diagnosed were examined for PKC isoform content by Western blot, immunohistochemistry, enzymatic activity, and in situ hybridization and compared with nonfailed left ventricle. Quantitative immunoblotting revealed significant increases of >40% in PKC-β1 (P<0.05) and -β2 (P<0.04) membrane expression in failed hearts compared with nonfailed; PKC-α expression was significantly elevated by 70% in membrane fractions (P<0.03). PKC-ε expression was not significantly changed. In failed left ventricle, PKC-β1 and -β2 immunostaining was intense throughout myocytes, compared with slight, scattered staining in nonfailed myocytes. PKC-α immunostaining was also more evident in cardiomyocytes from failed hearts with staining primarily localized to intercalated disks. In situ hybridization revealed increased PKC-β1 and -β2 mRNA expression in cardiomyocytes of failed heart tissue. PKC activity was significantly increased in membrane fractions from failed hearts compared with nonfailed (1021±189 versus 261±89 pmol · mg⁻¹ · min⁻¹, P<0.01). LY333531, a selective PKC-β inhibitor, significantly decreased PKC activity in membrane fractions from failed hearts by 209 pmol · min⁻¹ · mg⁻¹ (versus 42.5 pmol · min⁻¹ · mg⁻¹ in nonfailed, P<0.04), indicating a greater contribution of PKC-β to total PKC activity in failed hearts.

Conclusions—In failed human heart, PKC-β1 and -β2 expression and contribution to total PKC activity are significantly increased. This may signal a role for Ca²⁺-sensitive PKC isoforms in cardiac mechanisms involved in heart failure.