Calixarene C-90 selectively inhibits Ca2+,Mg2+-ATPase of myometrium cell plasma membrane
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The supramolecular compound calixarene C-90 (5,11,17,23-tetra(trifluoro)methyl(phenylsulfonylimino)-methylamino-25,26,27,28-tetrapropoxycalixarene) is shown to efficiently inhibit the ATP hydrolase activity of Ca2+,Mg2+-ATPase in the myometrium cell plasma membrane fraction and also in a preparation of the purified enzyme solubilized from this subcellular fraction. The inhibition coefficient I 0.5 values were 20.2 ± 0.5 and 58.5 ± 6.4 μM for the membrane fraction and the solubilized enzyme, respectively. The inhibitory effect of calixarene C-90 was selective comparatively to other ATPases localized in the plasma membrane: calixarene C-90 did not influence the activities of Na+,K+-ATPase and “basal” Mg2+-ATPase. The inhibitory effect of calixarene C-90 on the Ca2+,Mg2+-ATPase activity was associated with the cooperative action of four trifluoromethylphenyl sulfonylimine (sulfonylamidine) groups oriented similarly on the upper rim of the calixarene macrocycle (the calixarene “bowl”). The experimental findings seem to be of importance for studies, using calixarene C-90, of membrane mechanisms of regulation of calcium homeostasis in smooth muscle cells and also for investigation of the participation of the plasma membrane Ca2+-pump in control of electro- and pharmacomechanical coupling in myocytes.
Key wordsCa2+,Mg2+-ATPase plasma membrane calcium pump smooth muscle cells myometrium calixarenes sulfonylamidines
smooth muscular cells
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