Protein kinase A catalytic subunit alters cardiac mitochondrial redox state and membrane potential via the formation of reactive oxygen species

Background The identification of protein kinase A (PKA) anchoring proteins on mitochondria implies a direct effect of PKA on mitochondrial function. However, little is known about the relationship between PKA and mitochondrial metabolism. Methods and Results The effects of PKA on the mitochondrial redox state (flavin adenine dinucleotide (FAD)), mitochondrial membrane potential (Delta psi m) and reactive oxygen species (ROS) production were investigated in saponin-permeabilized rat cardiomyocytes. The PKA catalytic subunit (PKA(cat); 50 unit/ml) increased FAD intensities by 56.6 +/- 7.9% (p < 0.01), 2'7'-dichlorofluorescin diacetate (DCF) intensities by 10.5 +/- 3.3 fold (p < 0.01) and depolarized Delta psi(m) to 48.1 +/- 9.5% of the control (p < 0.01). Trolox (a ROS scavenger; 100 mu mol/L) inhibited PKA(cat)-induced Delta psi(m), FAD and DCF alteration. PKA(cat)-induced Delta psi(m) depolarization was inhibited by an inhibitor of the inner membrane anion channel (IMAC), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS: 1 mu mol/L) but not by an inhibitor of mitochondrial permeability transition pore (mPTP), cyclosporine A (100 nmol/L). Conclusions PKAcat alters FAD and AT via mitochodrial ROS generation, and PKA(cat)-induced Delta psi(m), depolarization was not caused by mPTP but rather by DIDS-sensitive mechanisms, which could be caused by opening of the IMAC. The effects of PKA on mitochondrial function could be related to myocardial function under the condition of extensive beta-adrenergic stimulation.