SELECTIVE SODIUM PUMP INHIBITOR CALIX[4]ARENE C-1130 INCREASES CONCENTRATION OF Ca IONS IN SMOOTH MUSCLE CELLS

Abstract

Aim. This work aimed to determine the biochemical regularities of calix[4]arene C-1130 effect on the activity of Nа+,К+-АТРase and Са2+ level in PM of smooth muscle cells (SMCs). Methods. Calix[4]arene C-1130 was synthesized and characterized in the Institute of Organic Chemistry of NAS of Ukraine. Biochemical studies were carried out in the Department of Muscle Biochemistry of Palladin Institute of Biochemistry, NAS of Ukraine. The experiments were performed on a suspension of myometrial cells and the PM fraction. Determination of the intracellular Са2+ concentration was done by confocal microscopy. The hydrodynamic diameter of myocytes was determined by dynamic light scattering. Results. We have studied the dependence of the activity of Nа+,К+-АТРase of PM on the concentration of Mg ions and ATP at different concentrations of calix[4]arene C-1130. The affinities of Nа+,К+-АТРase for ATP and Mg ions remained unaffected by the presence of calix[4]arene C-1130. However, a notable reduction in the initial maximum velocity of enzymatic ATP hydrolysis was observed. Overall, it indicates a non-competitive mechanism of inhibition of Nа+,К+-АТРase by C-1130. Confocal microscopy analysis showed that calix[4]arene C-1130 elevates Са2+ concentration within myometrial myocytes. Photon-correlation spectroscopy revealed that C-1130 reduces the effective hydrodynamic diameter of SMCs. Conclusions. We have shown that calix[4]arene C-1130 does not affect the activation coefficient for Mg ions and the apparent Michaelis constant Кm for ATP, but it reduces the maximum initial velocity Vmax of the ATP hydrolysis reaction. Thus, calix[4]arene C-1130 acts as a complete non-competitive inhibitor of Nа+,К+-АТРase of PM.