Т. О. Veklich¹, О. V. Tsymbalyuk², R. V. Rodik³,
O. V. Maliuk¹*, V. І. Kalchenko³, S. O. Kosterin¹,

¹Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv, Ukraine;
*e-mail: o.maliuk@biochem.kiev.ua;
²Educational and Scientific Institute of High Technologies,
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine;
^3Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kyiv, Ukraine

Received: 29 April 2026; Revised: 24 June 2026;
Accepted: 27 July 2026; Available on-line: August 2026

Background. Plasma membrane Na⁺,K⁺-ATPase plays an important role in maintaining ionic homeostasis and regulating myometrial contractility. Its inhibition may alter uterine smooth muscle responses to uterotonic stimulation. Objective. This study aimed to determine the mechanism by which calix[4]arene C-1130 inhibits Na⁺,K⁺-ATPase activity and to evaluate its effects on oxytocin-induced myometrial contractions. Methods. Na⁺,K⁺-ATPase activity was studied in suspensions of perforated plasma membranes isolated from myometrial cells. The kinetic parameters of ATP hydrolysis were determined at different ATP and Mg²⁺ concentrations. The effects of C-1130 on oxytocin-induced isometric and isotonic contractions were exami­ned in myometrial preparations with preserved endometrium. Results. Calix[4]arene C-1130 decreased the maximum rate of Na⁺,K⁺-ATPase-mediated ATP hydrolysis without significantly affecting the apparent affinity­ or cooperativity parameters for ATP and Mg²⁺. At a concentration of 10 μM, C-1130 enhanced oxytocin-induced isometric myometrial contraction and increased the normalized maximal rates of both contraction and relaxa­tion phases. Under isotonic conditions, C-1130 increased the velocity and enhanced the power characteris­tics of muscle contraction. Conclusions. Calix[4]arene C-1130 inhibits myometrial Na⁺,K⁺-ATPase­ through a noncompetitive mechanism. The enhancement of oxytocin-induced contractile muscle activi­ty is likely associated with disruption of ionic homeostasis in myocytes caused by inhibition of the plasma membrane Na⁺,K⁺-ATPase.