Inhibition of mitochondrial superoxide generation in rat alveolar macrophages by 12-O-tetradecanoylphorbol-13-acetate potential role of protein kinase C

We have observed that lucigenin-derived chemiluminescence (CL) measures superoxide anion (O₂) production from two major cellular compartments in rat alveolar macrophages (AMs): extracellular O₂/^- produced by NADPH oxidase; and intracellular O₂/^- produced by the reduction of molecular oxygen by the mitochondrial electron transport chain. Although the treatment of AMs with 30 ng/mL 12-O-tetradecanoyl phorbol-13-acetate (TPA) increases the production of O₂/^- by NADPH oxidase, the net result of TPA addition monitors is a decrease in lucigenin-derived CL resulting from inhibition of mitochondrial- derived O₂/^- production. Since protein kinase C (PKC) has been shown to be the cellular receptor through which TPA mediates its effects, it was postulated that activation of PKC inhibits mitochondrial-derived O₂/^- production as measured by lucigenin-derived CL. Studies performed with 50 μM H-7 (a PKC inhibitor) support this hypothesis by blocking the inhibition of mitochondrial-derived CL by TPA, while HA-1004, a negative control for H-7, had no effect on the system. These results suggest that mitochondrial respiration may be modulated by the actions of PKC. Moreover, this observation suggests a novel mechanism whereby chemicals which activate PKC may affect cellular function through modulation of mitochondrial activity.