Local control of mitochondrial membrane potential, permeability transition pore and reactive oxygen species by calcium and calmodulin in rat ventricular myocytes

Calmodulin (CaM) and Ca2+/CaM-dependent protein kinase II (CaMKII) play important roles in the development of heart failure. In this study, we evaluated the effects of CaM on mitochondrial membrane potential (ΔΨm), permeability transition pore (mPTP) and the production of reactive oxygen species (ROS) in permeabilized myocytes; our findings are as follows. (1) CaM depolarized ΔΨm dose-dependently, but this was prevented by an inhibitor of CaM (W-7) or CaMKII (autocamtide 2-related inhibitory peptide (AIP)). (2) CaM accelerated calcein leakage from mitochondria, indicating the opening of mPTP, however this was prevented by AIP. (3) Cyclosporin A (an inhibitor of the mPTP) inhibited both CaM-induced ΔΨm depolarization and calcein leakage. (4) CaM increased mitochondrial ROS, which was related to ΔΨm depolarization and the opening of mPTP. (5) Chelating of cytosolic Ca2+ by BAPTA, the depletion of SR Ca2+ by thapsigargin (an inhibitor of SERCA) and the inhibition of mitochondrial Ca2+ uniporter by Ru360 attenuated the effects of CaM on mitochondrial function. (6) CaM accelerated Ca2+ extrusion from mitochondria. We conclude that CaM/CaMKII depolarized ΔΨm and opened mPTP by increasing ROS production, and these effects were strictly regulated by the local increase in cytosolic Ca2+ concentration, initiated by Ca2+ releases from the SR. In addition, CaM was involved in the regulation of mitochondrial Ca2+ homeostasis.