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.