Effect of thyroid status on ouabain binding to the human lymphocyte.
Lymphocyte Na-K ATPase was evaluated as an index of thyroid status in man. Lymphocytes from 24 untreated hypothyroid patients and 11 hyperthyroid subjects were sampled in parallel with normal lymphocytes, and Na-K ATPase activity was assessed by measurements of ouabain binding to a plasma membrane fraction or to whole cells. In both systems, ouabain bound saturably and specifically, resulting in linear Scatchard plots. Normal lymphocyte plasma membranes bound 2.30 +/- 0.16 pmol ouabain/mg protein (mean +/- SEM; n = 11), with a Kd of 68 +/- 12 nM. Intact normal lymphocytes bound 3.24 +/- 0.30 pmol ouabain/10(7) cells (n = 14), representing 189,000 sites/cell. In hypothyroidism, ouabain binding, when compared with normal cells sampled on the same day, was reduced by 22.0 +/- 5.3% (n = 11; P less than 0.001) in plasma membranes and by 29.1 +/- 3.5% (n = 14) in whole lymphocytes (P less than 0.001), but there was no significant change in the Kd in the membrane fraction. In 6 subjects, the decrease in ouabain binding to lymphocytes was reversed by thyroid hormone replacement. Red cells from hypothyroid subjects showed normal ouabain binding. Ouabain binding to hyperthyroid plasma membranes (2.42 +/- 0.18 pmol/mg protein) was not significantly different from normal. The results in hypothyroid subjects are consistent with the hypothesis that lymphocyte Na-K ATPase is regulated by thyroid hormones. However, lymphocyte Na-K ATPase does not increase in parallel with elevated thyroid hormone levels in hyperthyroidism. The mechanisms underlying these observations remain to be clarified.
D000328:Adult; D000368:Aged; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood*; D007037:Hypothyroidism / Q000097:blood*; D007700:Kinetics; D008214:Lymphocytes / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010042:Ouabain / Q000097:blood*; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood
D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase