Role of mitochondrial permeability transition in taurine deficiency-induced apoptosis

It has recently been shown that taurine deficiency leads to impaired respiratory chain function, resulting in reduced ATP generation and enhanced oxidative stress. Because cardiomyopathy develops in taurine-deficient animals, the hypothesis that mitochondrial oxidative stress may contribute to the development of cardiomyocyte dysfunction and cell death was tested. Isolated neonatal cardiomyocytes incubated in medium containing the taurine transport inhibitor, beta-alanine, lost nearly one-half of their cellular taurine content after 48 h. Accompanying the loss of taurine was a time-dependent increase in apoptosis, which was prevented by the mitochondrial permeability transition inhibitor, cyclosporin A. Two taurine-dependent factors, oxidative stress and calcium overload, serve as important regulators of the mitochondrial permeability transition. Although taurine deficiency slowed the removal of calcium from the cytosol, it had no effect on diastolic calcium content and only modestly reduced systolic calcium content, suggesting that calcium overload is not the trigger for mitochondrial permeability transition pore formation. On the other hand, the glutathione redox ratio was significantly altered in the taurine-deficient cardiomyocyte, suggesting that oxidative stress is the primary initiator of mitochondrial permeability transition and apoptosis in the taurine-deficient cardiomyocyte.