Pharmacological and biochemical characterization of A 3 adenosine receptors in Jurkat T cells

The present work was devoted to the study of A 3 adenosine receptors in Jurkat cells, a human leukemia line. The A 3 subtype was found by means of RT‐PCR experiments and characterized by using the new A 3 adenosine receptor antagonist [ 3 H]‐MRE 3008F20, the only A 3 selective radioligand currently available. Saturation experiments revealed a single high affinity binding site with K D of 1.9±0.2 n M and B max of 1.3±0.1 pmol mg −1 of protein. The pharmacological profile of [ 3 H]‐MRE 3008F20 binding on Jurkat cells was established using typical adenosine ligands which displayed a rank order of potency typical of the A 3 subtype. Thermodynamic data indicated that [ 3 H]‐MRE 3008F20 binding to A 3 subtype in Jurkat cells was entropy‐ and enthalpy‐driven, according with that found in cells expressing the recombinant human A 3 subtype. In functional assays the high affinity A 3 agonists Cl‐IB‐MECA and IB‐MECA were able to inhibit cyclic AMP accumulation and stimulate Ca 2+ release from intracellular Ca 2+ pools followed by Ca 2+ influx. The presence of the other adenosine subtypes was investigated in Jurkat cells. A 1 receptors were characterized using [ 3 H]‐DPCPX binding with a K D of 0.9±0.1 n M and B max of 42±3 fmol mg −1 of protein. A 2A receptors were studied with [ 3 H]‐SCH 58261 binding and revealed a K D of 2.5±0.3 n M and a B max of 1.4±0.2 pmol mg −1 of protein. In conclusion, by means of the first antagonist radioligand [ 3 H]‐MRE 3008F20 we could demonstrate the existence of functional A 3 receptors on Jurkat cells.British Journal of Pharmacology (2001) 134 , 116–126; doi: 10.1038/sj.bjp.0704254