Thapsigargin-resistant thiacalix[4]arene C-1087-sensitive component of the contractile activity in rat myometrium reflects the functioning of plasma membrane calcium pump

Abstract

Background. According to existing knowledge, thiacalix[4]arene С-1087 is highly capable of inhibiting Са2+-pump (Са2+, Mg2+-АТРase) of the plasma membrane; at the same time it inhibits the functioning of Са2+-pump of the sarcoplasmic reticulum of uterine smooth muscles to some degree. The aim of this research was to study the effects of С-1087 on the concentration of Ca2+ ions and contractile activity of the rat myometrium cells using an inhibitor of Са2+-pump of the sarcoplasmic reticulum – thapsigargin. Materials and Methods. The experiments were conducted using outbred white non-pregnant rats. The contractile activity in the preparations of longitudinal SM of uterine horns with preserved endothelium was registered in the isometric mode. To determine the changes in [Ca2+]i level, myocytes were treated with probes Hoechst 33342 (to test the nucleus of the cell) and fluo-4 AM (to test the change in Са2+-concentration in the cell). Results. The tenzometric studies with the subsequent mechanokinetic analysis demonstrated that under the action of thapsigargin (0.5 µM), thiacalix[4]arene C-1087 (10 µM) caused considerable changes in the kinetics of the spontaneous contractile activity processes in the myometrium of rats, including the decrease in the maximal contraction velocity and the increase in the maximal relaxation velocity. By means of confocal microscopy with Ca2+-sensitive fluorescent probe fluo-4, it was demonstrated that the application of thiacalix[4]arene С-1087 to immobilized myocytes of the uterus against the background of thapsigargin caused a transient spike of Са2+-signal with the subsequent turn of the intracellular concentration of Ca ions to the stable increased level. The effects of С-1087 under the action of thapsigargin regarding the relaxation phase in the spontaneous myometrium contractions were removed after the preliminary blocking of nitric oxide synthases L-NAME (100 µM). Under the action of L-NAME, thiacalix[4]arene С-1087 (10 µM) caused complete inhibition of the relaxation process in the contraction of myometrium preparations, induced by high-potassium solution (80 mM). Conclusions. The primary reason for changes in the contractile activity and Ca2+-signal in uterine myocytes under the effect of thiacalix[4]arene С-1087 is its ability to inhibit Са2+-pump of the plasma membrane; further С-1087-induced changes in the smooth muscle tissues may be caused by the increased level of Са2+ concentration in myocytes. The obtained results demonstrate thiacalix[4]arene С-1087 is a promising compound for the elaboration of pharmacological preparations for modulating the contractile activity in smooth muscles, including myometrium.