A method for analysis of cellular K-transport mechanisms through thallium (201Tl) uptake in human lymphocytes

Thallium (Tl) is the K-congener with the highest specific affinity to K-binding sites and the largest permeability in K-channels, and its usefulness for analysis of cellular K-transport mechanisms was investigated. The uptake of 201Tl was measured in cultured human lymphocytes (Jurkat cells and EBV-transformed B-cells) after various incubation conditions. In a complete culture medium the half-time of the Tl-uptake was 10 min at 37 degrees C and the steady state accumulation ratio (intracellular/extracellular) was c. 50. The steady state ouabain sensitive uptake was 81% in complete culture medium, it was reduced after substitution with Ringer solution and by a decrease in temperature (from 37 to 22 degrees C). The ouabain resistant uptake was higher at 22 degrees C than at 37 degrees C and it was almost completely inhibited in Na-free or Cl-free solution and by furosemide. The present results indicate that there are only two major routes for K-uptake in lymphocytes and that 201Tl may be a useful substitute for K in the analysis of cellular K-transport mechanisms.