Age-Associated Mitochondrial Dysfunction in the Heart Accompanied by Constitutive NO-Synthases Uncoupling on the Background of Oxidative and Nitrosative Stress

Abstract

We investigated the sensitivity of mitochondrial permeability transition pore (MPTP) opening to its inductor calcium and indicators of oxidative and nitrosative stress in the heart mitochondria and heart tissues of adult and old rats. The coupling index of constitutive Ca2+/calmodulin-dependent NO-synthase (cNOS) was calculated based on experimentally found parameters. It has been revealed that aging, which is characterized by oxidative and nitrosative stress, is accompanied by a decrease of cNOS coupling index and an increase of MPTP sensitivity to calcium. We also found increased levels of oxidative stress in the heart mitochondria of old rats. In particular, the rate of superoxide (·O2−) and hydroxyl (·OH) generation increased by 4 and 2.7 times, respectively, the levels of urea and products of early lipid peroxidation (diene conjugates) increased by ten times, indicating the intensification of oxidative stress. Simultaneously, we observed enhanced nitrosative stress, as evidenced by an increase of nitrate reductase and iNOS activities. At the same time, the pools of NO2− and lowmolecular weight nitrosothiols, usually generated when the heart oxygenation is normal, as well as Ca2+/calmodulin-dependent cNOS activity were reduced. The latter was due to enhanced cNOS uncoupling, which resulted in oxidative stress enhancement. In addition, hydrogen sulphide (H2S) level decreased significantly in the heart mitochondria of old rats. Against the background of those processes, we observed an increased MPTP sensitivity to calcium, induced by a decrease in the concentration of nitric oxide and hydrogen sulphide as the inhibitory agents for MPTP, and an increase in the levels of ROS and RNS as inducers of its opening in the heart mitochondria of old rats.