ATP-sensitive potassium transport in rat brain mitochondria is highly sensitive to mK(ATP) channels openers: a light scattering study

The aspects of ATP-sensitive K+ transport regulation by mitochondrial K+,ATP-sensitive (mKATP) channels openers are important for understanding the properties of these channels. The effect of KATP channels openers (KCOs) diazoxide and pinacidil on ATP-sensitive K+ transport in isolated brain mitochondria was studied in the absence and the presence of MgATP using light scattering technique. Without MgATP we observed high sensitivity of ATP-sensitive K+ transport to both drugs with full activation at ≤ 0.5 µM. ATP-sensitive K+ transport was specifically blocked by ATP in the presence of Mg2+. Neither Mg2+ nor ATP affected Vmax of ATP-sensitive K+ transport activated by KCOs, but MgATP shifted the activation curve to micromolar scale. The blockage of ATP-sensitive K+ transport by KATP channels blockers glibenclamide and 5-hydroxydecanoate in the absence and the presence of MgATP proved the sensitivity of ATP-sensitive K+ transport to the blockers of mKATP channel. Full activation of mKATP channel by diazoxide and pinacidil on sub-micromolar scale in the absence of MgATP was shown. The sensitivity of ATP-sensitive K+ transport to the known modulators of mKATP channel (diazoxide, pinacidil, glibenclamide, 5-HD and MgATP) proved the identity of ATP-sensitive K+ transport with mKATP channel activity. Based on our studies, we hypothesized that mKATP channel might comprise high affinity sites for KCOs binding screened by MgATP. The results of this work reveal novel not described earlier aspects of the regulation of ATP-sensitive K+ transport by mKATP channels openers, important for understanding of mKATP channel properties

Estimation of ATP-dependent K(+)-channel contribution to potential-dependent potassium uptake in the rat brain mitochondria

The effect of potassium on state 4 respiration (substrate oxidation in the absence of ADP) was investigated. It was shown that potential-dependent potassium uptake in the brain mitochondria results in mitochondrial depolarization. Taking into account depolarization effect of potassium, the contribution of the endo­genous proton leak as well as K+-uptake to the re­spiration rate was calculated. It was shown that such estimation allows the share of ATP-dependent potassium channel contribution to potential-dependent potassium uptake to be determined by polarographic method

The effect of ATP-dependent K(+)-channel opener on transmembrane potassium exchange and reactive oxygen species production upon the opening of mitochondrial pore

The effect of mitochondrial ATP-dependent K+-channel (K+ATP-channel) opener diazoxide (DZ) on transmembrane potassium exchange and reactive oxygen species (ROS) formation under the opening of mitochondrial permeability transition pore (MPTP) was studied in rat liver mitochondria. The activation of K+-cycling (K+-uptake and K+/H+-exchange) by DZ was established with peak effect at ≤500 nM. It was shown that MPTP opening as well resulted in the activation of K+-cycling together with simultaneous activation of Ca2+-cycle in mitochondria. In the absence of depolarization Ca2+-cycle is supported by MPTP and Ca2+-uniporter. The stimulation of K+/H+-exchange by MPTP opening led to the activation of K+-cycle, but further activation of K+/H+-exchange resulted in MPTP inhibition. Under the same conditions the decrease in mitochondrial ROS production was observed. It was proposed that the decrease in ROS formation together with K+/Н+-exchange activation could be the constituents of the complex effect of MPTP inhibition induced by K+ATP-channel opener

The effect of ATP-dependent K(+)-channel opener on the functional state and the opening of cyclosporine-sensitive pore in rat liver mitochondria

The effect of mitochondrial ATP-dependent K+-channel (K+АТР-channel) opener diazoxide (DZ) on the oxygen consumption, functional state and the opening of cyclosporine-sensitive pore in the rat liver mitochondria has been studied. It has been established that K+АТР-channel activation results in the increase of the oxygen consumption rate (V4S) and the uncoupling due to the acceleration of K+-cycling, the decrease in state 3 respiration rate (V3) and the respiratory control ratio (RCR). Under K+АТР-channel activation an inhibition of oxidative phosphorylation takes place which reduces the rate of ATP synthesis and hydrolysis as well as ATP production and consequently results in the seeming increase of P/O ratio. It has been shown that the increase in ATP-dependent K+-uptake accompanied by the opening of mitochondrial permeability transition pore (MPTP) leads to dramatic uncoupling of the respiratory chain due to simultaneous activation of K+– and Ca2+-cycling supported by MPTP and Ca2+-uniporter as well as K+-channels and K+/H+-exchange. K+АТР-channel activation leads to the partial inhibition of MPTP, but insufficient for the restoration of mitochondrial functions. Elimination of Ca2+-cycling after MPTP opening is necessary to return mitochondrial functions back to the control level which shows that MPTP could serve as the mechanism of reversible modulation of bioenergetic effects of K+АТР-channel activation

Tryptophan Prevents the Development of Non-Alcoholic Fatty Liver Disease

Roman Yanko,1,* Mikhail Levashov,1,* Olena Georgievna Chaka,1 Valentina Nosar,1 Sergey G Khasabov,2 Iryna Khasabova2,* 1Department of Clinical Physiology of Connective Tissue, Bogomoletz Institute of Physiology National Academy of Sciences of Ukraine, Kiev, Ukraine; 2Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA*These authors contributed equally to this workCorrespondence: Roman Yanko, Department of Clinical Physiology of Connective Tissue, Bogomoletz Institute of Physiology National Academy of Sciences of Ukraine, Bogomoletz Street 4, Kiev, 01024, Ukraine, Tel +380442562477, Email [email protected]: The main aim of this research is to study the protective effects of tryptophan on the histomorphological and biochemical abnormalities in the liver caused by a high-calorie diet (HCD), as well as its ability to normalize mitochondrial functions in order to prevent the development of non-alcoholic fatty liver disease (NAFLD).Methods: The study was conducted in male Wistar rats aged 3 months at the start of the experiment. Control animals (group I) were fed a standard diet. Group II experimental animals were fed a diet with an excess of fat (45%) and carbohydrates (31%) for 12 weeks. Group III experimental animals also received L-tryptophan at a dose of 80 mg/kg body weight in addition to the HCD. The presence of NAFLD, functional activity, physiological regeneration, and the state of the liver parenchyma and connective tissue were assessed using physiological, morphological, histo-morphometric, biochemical, and biophysical research methods.Results: HCD induced the development of NAFLD, which is characterized by an increase in liver weight, hypertrophy of hepatocytes and an increase in the concentration of lipids, cholesterol and triglycerides in liver tissue. Increased alanine aminotransferase activity in the liver of obese rats also confirm hepatocytes damage. Tryptophan added to the diet lowered the severity of NAFLD by reducing fat accumulation and violations of bioelectric properties, and prevented a decrease in mitochondrial ATP synthesis.Conclusion: The addition of tryptophan can have a potential positive effect on the liver, reducing the severity of structural, biochemical, mitochondrial and bioelectric damage caused by HCD.Keywords: fatty liver disease, essential amino acids, obesit

The effect of potential-dependent potassium uptake on membrane potential in rat brain mitochondria

The effect of potential-dependent potassium uptake on the transmembrane potential difference (ΔΨm) in rat brain mitochondria has been studied­. It was shown that in potassium concentration range of 0-120 mM the potential-dependent K+-uptake into matrix leads to the increase in respiration rate and mitochondrial depolarization. ATP-dependent potassium channel (K+ATP-channel) blockers, gliben­clamide and 5-hydroxydecanoate, block ~35% of potential-dependent potassium uptake in the brain mitochondria. It was shown that K+ATP-channel blockage results in membrane repolarization by ~20% of control, which is consistent with experimental dependence of ΔΨm on the rate of potential-dependent potassium uptake. Obtained experimental data give the evidence that functional activity of K+ATP-channel is physiologically important in the regulation of membrane potential and energy-dependent processes in brain mitochondria