Substrate-dependent and cyclophilin D-independent regulation of mitochondrial flashes in skeletal and cardiac muscle.

Mitochondrial flashes (mitoflashes) are stochastic events in the mitochondrial matrix detected by mitochondrial-targeted cpYFP (mt-cpYFP). Mitoflashes are quantal bursts of reactive oxygen species (ROS) production accompanied by modest matrix alkalinization and depolarization of the mitochondrial membrane potential. Mitoflashes are fundamental events present in a wide range of cell types. To date, the precise mechanisms for mitoflash generation and termination remain elusive. Transient opening of the mitochondrial membrane permeability transition pore (mPTP) during a mitoflash is proposed to account for the mitochondrial membrane potential depolarization. Here, we set out to compare the tissue-specific effects of cyclophilin D (CypD)-deficiency and mitochondrial substrates on mitoflash activity in skeletal and cardiac muscle. In contrast to previous reports, we found that CypD knockout did not alter the mitoflash frequency or other mitoflash properties in acutely isolated cardiac myocytes, skeletal muscle fibers, or isolated mitochondria from skeletal muscle and the heart. However, in skeletal muscle fibers, CypD deficiency resulted in a parallel increase in both activity-dependent mitochondrial Ca