Inhibition of Na(+),K(+)-ATPase and activation of myosin ATPase by calix[4]arene C-107 cause stimulation of isolated smooth muscle contractile activity

The discovery of compounds that might modify myometrial contractility is an important area of researches. In our previous experiments, we found that some representatives of macrocyclic compounds fami­ly – calix[4]arenes – can modify the enzymatic and transport activity of membrane-bound cation-transport ATP hydrolases. The aim of this work was to study and compare the effect of calix[4]arene C-107 on the enzymatic activities of Mg2+-dependent ATPases of the uterine smooth muscle, namely: ouabain-sensitive Na+,K+-ATPase, plasma membrane Ca2+-independent “basal” Mg2+-ATPase, ATPase of the actomyosin complex and myosin subfragment-1, with effect on the contractile activity of the myometrium. It was shown that calix[4]arene C-107 efficiently inhibited myometrium Na+,K+-ATPase (I50 = 54 ± 6 nM) selectively to other ATP-hydrolases of the plasma membrane and simultaneously activated the enzymatic activity of the myosin ATPase of smooth muscles (A50 = 9.6 ± 0.7 μM). Such reciprocal biochemical effects led to the stimulation of the smooth muscle contractile activity that was demonstrated by the tensometric method using different isolated smooth muscles. Calix[4]arene С-107 was shown to stimulate the increase of the tonic component of myometrium contractions induced by oxytocin, as well as contractions of the caecum muscles induced by high-potassium solution or acetylcholine, and to maintain increased tension for a long time. Thus, calix[4]arene C-107 is a prospective compound for enhancing the smooth muscle basal tone and/or contraction in case of hypotonic dysfunctions

The сalix[4]arene C-107 is highly effective supramolecular inhibitor of the Na(+),K(+)-АТРase of plasmatic membrane

The inhibition of the Na+,K+-АТРase activity of the myometrium cell plasma membranes with calixarene С-107 (5,17-diamino(2-pyridyl)methylphosphono-11,23-di-tret-butyl-26,28-dihydroxy-25,27-dipropoxycalix[4]arene) was investigated. It has been shown that calixarene С-107 reduced the Na+,K+-АТРase activity more efficiently than ouabain did, while it did not practically influence the “basal” Mg2+-АТРase activity of the same membrane. The magnitude of the cofficient of inhibition I0.5 was 33 ± 4 nМ, Hill coefficient was 0.38 ± 0.06. The model calixa­rene C-150 – the calixarene “scaffold” (26,28-dihydroxy-25,27-dipropoxycalix[4]arene), and the model compound М-3 (4-hydroxyaniline(2-pyridine)methylphosphonic acid) – a fragment of the calixarene С-107, had practically no influence on the enzymatic activity of Na+,K+-АТРase and Mg2+-АТРаse. We carried out the computer simulation of interaction of calixarenes C-107 and the mentioned model compound with ligand binding sites of the Na+,K+-АТРase of plasma membrane and structure foundation of their intermolecular interaction was found out. The participation of hydrogen, hydrophobic, electrostatic and π-π (stacking) interaction between calixarene and enzyme aminoacid residues, some of which are located near the active center of Na+,K+-АТРase, was discussed