Identification of A2a receptors as the major type of adenosine receptor in mouse T lymphocytes. (A) Pharmacologic identification of A2a receptor as the major adenosine receptor in T lymphocytes. Specific A2a receptor agonist CGS21680 triggered cAMP accumulation in DBA-2 splenocytes, whereas specific A2a receptor antagonist CSC inhibited effects of CGS21680. DBA-2 mouse splenocytes (at 5 × 106 cells/mL, 200 μL per well) were preincubated with or without 20 μmol/L CSC and then incubated with different concentrations of CGS21680 at 37°C for 60 minutes. cAMP PDE inhibitor (50 μmol/L), IBMX, was included to prevent catabolism of accumulated cAMP. The levels of cAMP were estimated by enzyme-linked immunoassay as described in the Materials and Methods. (B) A2a mRNA, but not the A1 or A3 mRNA, is the major expressed adenosine receptor message in DBA-2 lymphocytes. Mouse T-cell mRNA was isolated and analyzed as described in the Materials and Methods. The A2a receptor message (2.4-kb transcript) is detected in the poly A RNA samples from mouse splenocytes, lane 1; lymph node cells, lane 2; mastocytoma cell RNA, lane 3; and mouse brain RNA, lane 4. The A1 and A3 mRNA messages were detected only in positive controls, mouse brain RNA and mastocytoma cell RNA, respectively.
