Tag Archives: oxygen consumption

Adaptive respiratory response of rat pancreatic acinar cells to mitochondrial membrane depolarization

B. O. Manko, O. O. Bilonoha, V. V. Manko

Ivan Franko National University of Lviv, Ukraine;
e-mail: bohdan.manko@lnu.edu.ua

Received: 06 December 2018; Accepted: 14 March 2019

The dependence of uncoupled respiratory capacity of intact pancreatic acini on oxidative substrate supply and functional cell state has not yet been studied in detail. In this study, the respiratory responses of isolated pancreatic acini to FCCP were measured with Clark electrode and mitochondrial membrane potential was assessed with rhodamine123 fluorescence. The response of acini to FCCP was characteri­zed with maximal uncoupled respiration rate, optimal FCCP concentration, respiration acceleration and decele­ration. Maximal uncoupled respiration rate substantially increased upon the oxidation of glucose + glutamine (3.03 ± 0.54 r.u.), glucose + glutamine + pyruvate (2.82 ± 0.51 r.u.), glucose + isocitrate (2.71 ± 0.33 r.u.), glucose + malate (2.75 ± 0.38 r.u.), glucose + monomethyl-succinate (2.64 ± 0.42 r.u.) or glucose + dimethyl-α-ketoglutarate (2.36 ± 0.33 r.u.) comparing to glucose alone (1.73–2.02 r.u.) or no substrate (1.76 ± 0.33 r.u.). The optimal FCCP concentration was the highest (1.75 μM) upon glucose + glutamine + pyruvate combination and the lowest (0.5 μM) upon glutamate, combinations of glucose with isocitrate, malate, succinate or α-ketoglutarate. Respiration acceleration after FCCP application was the highest with dimethyl-α-ketoglutarate. Following the peak respiration, time-dependent deceleration was observed. It increased with FCCP concentration and depended on oxidative substrate type. Deceleration was the highest upon malate or isocitrate oxidation but was not observed in case of glutamine or dimethyl-α-ketoglutarate oxidation. Pyruvate alone or in combination with glutamine and glucose significantly decreased the depolarizing effect of FCCP on mitochondrial membrane potential and increased respiration elasticity coefficient with respect to the membrane potential change. Thus, in pancreatic acinar cells, the combination of pyruvate, glutamine and glucose enables the optimal adaptive respiratory response to membrane depolarization.

The effect of Са(2+)-induced opening of cyclosporine-sensitive pore on the oxygen consumption and functional state of rat liver mitochondria

O. V. Akopova, V. I. Nosar, I. N. Mankovska, V. F. Sagach

A. A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv;
e-mail: a-dubensky@mail.ru

The effect of Ca2+-induced opening of cyclosporine-sensitive pore (mitochondrial permeability transition pore, MPTP) on the oxygen consumption and mitochondrial functional state was studied­ in the rat liver mitochondria. It was shown that, with the use of glutamate as oxidation substrate, in the absence of depolarization MPTP opening results in the increase of steady state respiration rate because of the activation of cyclosporine-sensitive Ca2+/H+-exchange and Ca2+ cycling, which was supported by the simultaneous work of MPTP and Ca2+-uniporter. With the aid of selective blockers, cyclosporine A and ruthenium red, it was shown that MPTP and Ca2+-uniporter contribute equally to the Ca2+-cycling and mitochondrial respiration. It was shown that bioenergetic effects of MPTP opening under steady state conditions (increase in the oxygen consumption rate under substrate oxidation without ADP, decrease in respiratory control ratio as well as the effectiveness of ATP synthesis, P/O) are close to the functional alterations, which result from the increase of endogenous proton conductance of mitochondrial membrane. Uncoupling effect of MPTP opening, by itself, had no effect on phosphorylation rate, which remains relatively stable because the fall of P/O is compensated by the activation of respiratory chain and the increase in the rate of state 3 respiration. It was concluded that under physiologically normal conditions MPTP might function as the endoge­nous mechanism of mild uncoupling of respiratory chain.

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

O. V. Akopova, V. I. Nosar, L. I. Kolchinskaya,
I. N. Mankovska, M. K. Malysheva, V. F. Sagach

Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv;
e-mail: luko@biph.kiev.ua

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.