Signaling via A2A adenosine receptor in four PC12 cell clones

PC12 cells are genetically labile and so-called wild-type cells comprise multiple subclones. We have examined the A(2A) adenosine receptor signal transduction pathways in four such clones (denoted clones 1, 19, 21 and 27) of PC12 cells. Adenosine A(2A), A(2B) and A(1) receptor mRNAs were detected in all four clones by RT-PCR, whereas no A(3) receptor mRNA was found. A(2A) receptors were quantitated by radioligand binding using the antagonist radioligand [H-3]SCH 58261 ([H-3]-5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4 triazolo[1,5-c] pyrimidine). The B-max was highest in clone 1 followed by clones 21, 19 and 27. Whereas the amount of G(i) protein appeared similar in all four clones, the amount of G(s) protein was higher in clones 21 and 27 than in the other two clones. Maximal responses to the non-selective adenosine analogue NECA (5'-N-ethylcarboxamidoadenosine) were similar to those observed with the selective adenosine A(2A) receptor agonist CGS 21680 (2-[p-(2-carbonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine), and were approximately equal in clones 1 and 21, but lower in clone 19 and very low in clone 27. For both compounds EC50 was significantly higher in clone 27 than in clone 1. In both clones the response to NECA could be competitively antagonized by a selective adenosine A(2A) antagonist, SCH 58261. The present results show that different clones of PC12 cells differ widely in the cAMP increase induced by adenosine analogues and that this is due to differences in the amount of adenosine A(2A) receptor, G protein and effector. A large difference in receptor number resulted in differences in potency of an agonist.