Subcellular distribution of protein kinase C isozymes during cardioplegic arrest

Background: On the basis of the hypothesis that cardioplegia-associated myocardial depression was due to activation of protein kinase C, we examined whether specific protein kinase C isozymes would translocate to a cellular fraction containing myofilaments. Methods: Isolated rat hearts were perfused with Krebs-Ringer bicarbonate buffer for 30 minutes and arrested with 4°C St Thomas No. 2 cardioplegic solution for 0 to 120 minutes (n = 5 per group). The 3 fractions of the left ventricle tissue represented the myofibrillar/nuclear fraction (P1), membranes (P2), and cytosol (supernatant). The distributions of protein kinase C isozymes α, δ, ε, and η were examined after separation by electrophoresis, immunoblotting/chemiluminescence, and densitometry. Results: A significant increase in protein kinase C-δ in the P1 fraction was detected after 5 minutes of cardioplegic arrest and remained increased for 60 minutes. Increases in P1 protein kinase C-α and -ε were seen transiently at 5 minutes, and protein kinase C-ε demonstrated a secondary increase in P1 at 30 to 60 minutes. There was also a significant relative increase in protein kinase C-α and protein kinase C-δ in the P2 fraction after 60 minutes of cardioplegia. Conclusions: These data are consistent with our hypothesis that activation of protein kinase C isozymes is associated with altered myofilament function after cardioplegic arrest.