STIMULATION OF THE NA+, K+-ATPASE ACTIVITY OF K562 HUMAN ERYTHROLEUKEMIA-CELLS BY TRIIODOTHYRONINE

The effect of triiodothyronine (T3) on Na+,K+-ATPase activity of K562 human erythroleukemic cell was studied to understand why the erythrocyte sodium pump activity is decreased in hyperthyroidism. Na+,K+-ATPase activity of K562 cell lysates was assayed by measuring the release of inorganic phosphate (Pi) from ATP. Na+,K+-ATPase activity of K562 cell grown in the presence of T3 for 48 hours was significantly higher than that of control (0.98 +/- 0.05 mumol Pi h-1 mg protein-1 vs 0.82 +/- 0.10 mumol Pi h-1 mg protein-1, p < 0.05). The N+,K+-ATPase activity could be stimulated in a time- and concentration-dependent manner; maximum stimulatory effect of T3 was seen at a concentration of 10(-7) mol/L. When an inducer [cytosine-beta-D-arabino-furanoside (ARA-C)] was added to the culture medium, the K562 cells showed signs of differentiation and synthesised haemoglobin. At the same time, the Na+,K+-ATPase activity remained high. We conclude that T3 stimulates Na+,K+-ATPase activity of K562 cells and in the presence of T3 during differentiation, the enzyme activity remains high.