S. G. Shlykov¹*, L. G. Babich¹, A. I. Panchenko¹, R. V. Rodik², S. G. Vyshnevskiy², V. I. Kalchenko², S. O. Kosterin¹

¹Department of Muscle Biochemistry, Palladin Institute of Biochemistry,
National Academy of Sciences of Ukraine, Kyiv, Ukraine;
²Department of Chemistry of Macrocyclic Compounds, Institute of Organic Chemistry,
National Academy of Sciences of Ukraine, Kyiv, Ukraine;
*e-mail: sshlykov@biochem.kiev.ua

Received: 12 May 2026; Revised: 24 June 2026;
Accepted: 27 July 2026; Available on-line: August 2026

Background. Calixarenes are supramolecular compounds with a unique three-dimensional structure, the biological activity of which is determined by the chemical groups on the upper or lower rim. It was found that thiacalix[4]arene C-1087 selectively (compared to other ATPases) inhibits plasma membrane Ca²⁺,Mg²⁺-ATPase activity that playіs a crucial role in maintaining Ca²⁺ homeostasis in myometrial cell. To expand our understanding of the thiacalix[4]arene C-1087 effects on Ca²⁺ exchange in myometrial cells, it is necessary to analyze its possible effects on Ca²⁺ exchange in intracellular pools. Objective. Therefore, the aim of this study was to investigate whether thiacalix[4]arene C-1087 affects Ca ion exchange in myometrial mitochondria. Methods. Mitochondria from myometrium of non-pregnant rats were isolated. Ionized calcium concentration in the mitochondria matrix was determined using the fluorescent probe Fluo-4 AM. Baseline Ca²⁺ concentration in the absence of exogenous (added) Ca²⁺ and Ca²⁺ accumulation in its presence were determined. Ca²⁺ concentration in the incubation medium was determined using fluorescent probe 1 µM Fluo5F, Pentapotassium Salt. Relative value of mitochondria membrane potential (Δψ) was assayed using a fluorescent probe 100 nM TMRM. The Microsoft Office Excel software package was used for data processing. Results. It was proven that mitochondria incubation in Mg²⁺– and Mg²⁺,АТР-medium with 10 μM thiacalix[4]arene C-1087 was accompanied by an increase of both the baseline Са²⁺ concentration and accumulation of this cation in the matrix and did not affect Са²⁺ efflux from mitochondria. Mitochondria incubation with 10 μM thiacalix[4]arene C-1087 resulted in reducing of TMRM-loaded mitochondria fluorescence intensity, indicatings the depolarizing effect of this compound. Conclusions. The results obtained indicate the possibility of thiacalix[4]arene C-1087 modulating effect on the Са²⁺ exchange in mitochondria and polarization of its membranes.