Characteristics of a (Na+-K+)-ATPase inhibitor in extracts of tea

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Abstract
Extracts of tea were examined for inhibitors of the sodium-potassium pump by investigating the effect of the extracts on 1) isolated preparations of (Na+-K+)-ATPase from hog brain and human blood cells; 2) the displacement of radioactive ouabain from its specific receptor on red blood cells, and 3) the uptake of radioactive rubidium in intact red blood cells. It has been found that extracts of tea were potent inhibitors of the purified hog brain (Na+-K+)-ATPase. However, the inhibition was not specific for the (Na+-K+)-ATPase and the extract of tea did not displace 3H-ouabain in a specific ouabain-receptor assay. Additionally, the tea extracts displayed only a small inhibitory effect on the uptake of 86Rb in intact red blood cells. These observations suggest that the material is not like digitalis and that, unlike cardiac glycosides, it may inhibit the activity of the (Na+-K+)-ATPase by interacting with the enzyme at intracellular sites.