Inhibition by quercetin of thyroid hormone stimulation in vitro of human red blood cell Ca2+-ATPase activity.
Human red blood cell membrane Ca2+-ATPase activity is stimulated in vitro by physiological concentrations of thyroid hormone. Quercetin, a flavonoid that inhibits several membrane-linked ATPases, suppressed thyroid hormone action on red cell Ca2+-ATPase activity and also interfered with binding of the hormone by red cell membranes. These effects of quercetin were dose-dependent over a range of concentrations (1-50 microM). In contrast, in the absence of thyroid hormone, quercetin at low concentrations stimulated Ca2+-ATPase activity and at 50 microM inhibited the enzyme. The effects of quercetin at low concentrations (1-10 microM), namely, stimulation of Ca2+-ATPase and inhibition of membrane-binding of thyroid hormone, mimic those of thyroid hormone and are consistent with the thyronine-like structure of quercetin. At high concentrations, quercetin is generally inhibitory of Ca2+-ATPase activity. Chalcone, fisetin, hesperetin and tangeretin are other flavonoids shown to reduce susceptibility of membrane Ca2+-ATPase to hormonal stimulation.
D000252:Calcium-Transporting ATPases / Q000097:blood*; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D011794:Quercetin / Q000494:pharmacology*; D013974:Thyroxine / Q000494:pharmacology*
D005419:Flavonoids; D011794:Quercetin; D000252:Calcium-Transporting ATPases; D013974:Thyroxine