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

1 The present work was devoted to the study of A(3) adenosine receptors in Jurkat cells, a human leukemia line. 2 The A(3) subtype was found by means of RT-PCR experiments and characteriz ed by using the new A(3) adenosine receptor antagonist [H-3]-MRE 3008F20, t he only A(3) selective radioligand currently available. Saturation experime nts revealed a single high affinity binding site with K-D of 1.9 +/-0.2 nM and B-max of 1.3 +/-0.1 pniol mg(-1) of protein. 3 The pharmacological profile of [H-3]-MRE 3008F20 binding on Jurkat cells was established using typical adenosine ligands which displayed a rank orde r of potency typical of the A3 subtype. 4 Thermodynamic data indicated that [H-3]-MRE 3008F20 binding to A(3) subty pe in Jurkat cells was entropy- and enthalpy-driven, according with that fo und in cells expressing the recombinant human A(3) subtype. 5 In functional assays the high affinity A(3) agonists Cl-IB-MECA and IB-ME CA were able to inhibit cyclic AMP accumulation and stimulate Ca2+ release from intracellular Ca2+ pools followed by Ca2+ influx. 6 The presence of the other adenosine subtypes was investigated in Jurkat c ells. A(1) receptors were characterized using [H-3]-DPCPX binding with a K- D of 0.9 +/-0.1 nM and B-max of 42 +/-3 fmol mg(-1) of protein. A(2A) recep tors were studied with [H-3]-SCH 58261 binding and revealed a K-D of 2.5 +/ -0.3 nM and a B-max of 1.4 +/-0.2 pmol mg(-1) of protein. 7 In conclusion, by means of the first antagonist radioligand [H-3]-MRE 300 8F20 we could demonstrate the existence of functional A(3) receptors on Jur kat cells.