Tag Archives: Са(2+)

Regulation of ionized calcium concentration in mitochondria matrix in the absence of exogenous Са(2+)

A. V. Sylenko*, S. G. Shlykov, L. G. Babich,
О. Yu. Chunikhin, S. O. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
*e-mail: sylenkoanna@ukr.net

Received: 15 September 2021; Accepted: 17 May 2021

Functional activity of mitochondria depends on ionized calcium content in its matrix. Thus, investigation of the ways to influence Ca2+ transport and accumulation in these organelles is an urgent issue. The aim of this work was to evaluate  ionized calcium concentration in the mitochondria matrix in the absence of exoge­nous Ca2+ and in the presence of Mg2+ and ATP in incubation media. The concentration of ionized calcium in mitochondria isolated from the myometrium of non-pregnant rats was measured with the fluorescent probe Fluo-4 AM, mitochondria hydrodynamic diameter was assessed using dynamic light scattering. The ATP concentration-dependent increase in ionized calcium concentration in mitochondria matrix in the absence of exogenous Са2+ and the high level of the total Са2+ accumulation after further addition of exogenous Са2+ were registered. The effect of ATP on Са2+ concentration did not depend on the blockage of mitochondrial PTP with cyclosporine A or on H+-ATPase/ATP-synthase inhibition with oligomycin, instead the addition of 10mM theophylline and 30 mM NaHCO3 to the Mg2+-containing medium led to Са2+ concentration elevation in mitochondria matrix. It was shown that low Ca2+ concentration in the matrix correlated with the increase in mitochondria size, whereas high Ca2+ concentration correlated with relatively smaller size of the organelles. Activation of the soluble adenylyl cyclase by NaHCO3 with simultaneous inhibition of phosphodiesterase by theophylline was accompanied by the decline in Са2+ probe normalized fluorescence in mitochondria matrix under conditions of exogenous Ca2+ introduction. It was suggested that the soluble adenylyl cyclase may be involved in regulation of Са2+ concentration in mitochondria matrix.

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.