PT - JOURNAL ARTICLE AU - Stefania Gessi AU - Katia Varani AU - Stefania Merighi AU - Elena Cattabriga AU - Arianna Avitabile AU - Riccardo Gavioli AU - Cinzia Fortini AU - Edward Leung AU - Stephen Mac Lennan AU - Pier Andrea Borea TI - Expression of A<sub>3</sub> Adenosine Receptors in Human Lymphocytes: Up-Regulation in T Cell Activation AID - 10.1124/mol.65.3.711 DP - 2004 Mar 01 TA - Molecular Pharmacology PG - 711--719 VI - 65 IP - 3 4099 - http://molpharm.aspetjournals.org/content/65/3/711.short 4100 - http://molpharm.aspetjournals.org/content/65/3/711.full SO - Mol Pharmacol2004 Mar 01; 65 AB - The present study investigates mRNA and protein levels of A3 adenosine receptors in resting (R) and activated (A) human lymphocytes. The receptors were evaluated by the antagonist radioligand [3H]5-N-(4-methoxyphenyl-carbamoyl)amino-8-propyl-2(2furyl)-pyrazolo-[4,3e]-1,2,4-triazolo-[1,5-c]-pyrimidine ([3H]MRE 3008F20), which yielded Bmax values of 125 ± 15 and 225 ± 23 fmol/mg of protein and KD values of 1.79 ± 0.30 and 1.85 ± 0.25 nM in R and A cells, respectively. The protein seems to be induced with remarkable rapidity starting at 15 min and reaches a plateau at 30 min. Western blot assays revealed that the up-regulation of the A3 subtype after lymphocyte activation was caused by an increase in an enriched CD4+ cell fraction. Real-time reverse transcription-polymerase chain reaction experiments confirmed the rapid increase of A3 mRNA after T cell activation. Competition of radioligand binding by adenosine ligands displayed a rank order of potency typical of the A3 subtype. Thermodynamic data indicated that the binding is enthalpy- and entropy-driven in both R and A cells, suggesting that the activation process does not involve, at a molecular level, receptor alterations leading to modifications in the A3-related binding mechanisms. Functionally, the up-regulation of A3 adenosine receptors in A versus R cells corresponded to a potency increase of the A3 agonist N6-(3-iodo-benzyl)-2-chloro-adenosine-5′-N-methyluronamide in inhibiting cAMP accumulation (IC50 = 1.5 ± 0.4 and 2.7 ± 0.3 nM, respectively); this effect was antagonized by MRE 3008F20 (IC50 = 5.0 ± 0.3 nM). In conclusion, our results provide, for the first time, an in-depth investigation of A3 receptors in human lymphocytes and demonstrate that, under activating conditions, they are up-regulated and may contribute to the effects triggered by adenosine.