Luchkova A. The role of hydrogen sulfide (H2S) in the regulation of calcium homeostasis and mitochondrial functions in adult and old rats.

Thesis for obtaining the degree of Doctor of Philosophy (PhD) in Biological Sciences, speciality 03.00.13. - Human and animal physiology. – Bogomolets Institute of Physiology of NAS of Ukraine, Kyiv, 2020 The dissertation is devoted to the study of the role of hydrogen sulfide (H2S) as an endogenous regulatory molecule of calcium homeostasis in the heart mitochondria of adult and old rats. Using the inhibitor of mitochondrial H2S synthesis enzyme decreased the H2S content in mitochondria and blood plasma. At the same time cardiodynamic indexes, including left ventricle pressure and the rate of contraction and relaxation of the myocardium were reduced twice, and the coronary flow (CF) by 11.8%. Under conditions of calcium loading, the hearts of experimental animals developed weaker reaction, which was manifested in decreased values of LVP, contractile activity, CF and myocardial work. Maximum inotropic stimulation of the heart in control animals was observed in response to the addition of 7.5 mmol/l CaCl2, whereas in the experimental - at 5 mmol/l CaCl2. This indicates a decrease in myocardial functional reserves in animals under conditions of inhibition of the synthesis of hydrogen sulfide. It was also found that under conditions of inhibition of hydrogen sulfide synthesis, oxidative stress indicators, such as superoxide and hydroxyl radicals increased as lipid peroxidation and activity of iNOS, against the decreased functional activity of cNOS in rat heart mitochondria. It was first discovered that exogenous hydrogen sulfide (10-6 -10-7 mol/l) increases Ca2+ uptake into the mitochondria of adult and old rat heart under calcium loading, with 10-5 mol/l NaHS preventing mitochondrial pore opening in organelles. This demonstrates the regulation of Ca2+ transport in mitochondria by hydrogen sulfide and is the important fundamental discovery. At the same time, inhibition of endogenous H2S formation in vivo reduces the threshold of sensitivity of the mitochondrial pore to Ca2+ and increases the swelling amplitude of adult and old rat heart mitochondria. It was shown for the first time that inhibition of the mitochondrial in vivo reduced the functional ability of the mitochondrial electron transport chain, which was manifested in the decrease of oxygen consumption rate in the states V2, V3 and V4, as well as indicators of respiratory control and ADP/O. Therefore, endogenous hydrogen sulfide regulates calcium transport in mitochondria, performs an antioxidant role and supports the work of the electron transport chain in mitochondria of the heart of rats of all ages.