FUNCTIONAL-CHARACTERIZATION OF ADENOSINE A(2) RECEPTORS IN JURKAT CELLS AND PC12 CELLS USING ADENOSINE RECEPTOR AGONISTS

The effect of several adenosine analogues on cyclic AMP accumulation w as examined in the rat phaeochromocytoma cell PC12 and in the human T- cell leukaemia cell Jurkat, selected as prototypes of cells predominan tly expressing adenosine A(2A) or A(2B) receptors. Using the reverse t ranscription-polymerase chain reaction it was, however, demonstrated t hat the Jurkat cell and the PC12 cell express both A(2A) and A(2B) rec eptor mRNA, albeit in different relative proportions. In PC12 cells th e concentration required for half-maximal response (EC(50)) for the fu ll agonist 5'-N-ethyl-carboxamidoadenosine (NECA) was 30 times lower t han in Jurkat cells, There was no significant difference in the pA(2) for the antagonist ,4-triazolo(1,5-C)quinazolinemonomethanesulphonate (CGS 15943) between the two cell types. In the presence of forskolin ( 1 mu M in PC12 cells; 10 mu M in Jurkat cells) the EC(50) value for NE CA was reduced two-to sixfold. Forskolin also increased the maximal cA MP accumulation twofold in PC12 cells and sevenfold in Jurkat cells. A series of 2-substituted adenosine analogues CV 1808 (2-phenylamino ad enosine), CV 1674 [2-(4-methoxyphenyl)adenosine], CGS 21680 onylethyl) phenylethylamino]-5'-N-ethyl-carboxamido adenosine}, and four 2-substi tuted isoguanosines, SHA 40 [2-(2-phenylethoxy)adenosine; PEA], SHA 91 [2-(2-cyclohexylethoxy)adenosine; CEA], SHA 118 {2-[2-(p-methylphenyl )ethoxy]adenosine; MPEA} and SHA 125 (2-hexyloxyadenosine; HOA), all r aised cAMP accumulation in PC12 cells, but had minimal or no effect in Jurkat cells. In the PC12 cells the addition of forskolin (1 mu M) re duced the EC(50) by a factor of 2 (CV 1808) to 12 (SHA 125). In Jurkat cells all the analogues gave a significant, but submaximal, cAMP resp onse in the presence of forskolin (10 mu M), but they were essentially inactive in its absence. The results show that a series of 2-substitu ted adenosine analogues can be used to discriminate between A(2A) and A(2B) receptors. The two receptor subtypes appear to coexist, even in clonal cells selected for typical pharmacology. A(2) receptor pharmaco logy can therefore be complex.