MITOCHONDRIAL DYSFUNCTION IN THE AGING HEART IS 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, as well as indicators of oxidative and nitrosative stress in adult and old rat heart mitochondria and heart tissues. The coupling index of constitutive Ca2+/calmodulin-dependent NO-synthase (сNOS) was calculated based on experimentally found parameters. The aging is characterized by oxidative and nitrosative stress, which accompanied by a decrease of the cNOS coupling index and an increased sensitivity of MPTP to calcium. We found that in the heart mitochondria of old rats such oxidative stress indicators as the rate of generation of superoxide (• O2 - ) and hydroxyl (• OH) anion radicals were significantly increased (in 4 and 2,7 times respectively). Also, increased levels of urea and products of early lipid peroxidation – conjugated dienes display the intensification of oxidative stress. Such indicators of nitrosative stress as nitrate reductase and iNOS activity were also enhanced. At the same time under aging the NO2 - pools, generated when the heart oxygenation is normal, nitrosothiols pools and the activity of cNOS were decreased. It is due to the enhanced level of cNOS uncoupling, resulting in increased oxidative stress. It was also shown the lower level of hydrogen sulfide (H2S) in old rat heart mitochondria. Thus, we observed the increased sensitivity of MPTP to calcium, due to decreased concentration of its inhibitors nitric oxide and hydrogen sulfide and increased levels of its inducers ROS and RNS in old rat heart mitochondria.