Anoxia redistributes adenosine A2A receptors in PC12 cells and increases receptor-mediated formation of cAMP

Undifferentiated and NGF-treated PC12 cells were subjected to anoxia for up to 24 h. The adenosine A(2A) receptor antagonist 5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4 triazolo[1,5-c]pyrimidine (SCH 58261) decreased viability of undifferentiated, but not NGF-treated PC12 cells after 6 h of anoxia. Anoxia also transiently enhanced cAMP responses induced via activation of adenosine A(2A) receptors in undifferentiated PC12 cells (20-fold decrease in the EC50 value for the agonist 2-[p-(2-carbonylethyl) phenylethylamino]-5'-N-ethylcarboxamidoadenosine, CGS 21680). In NGF-treated PC12 cells, by contrast, anoxia decreased both the maximal response to and the potency of CGS 21680. In undifferentiated PC12 cells subjected to anoxia a very modest increase of A(2A) receptor mRNA was detected in cells by Northern blotting, but no changes in the amount of the receptor protein could be seen by Western blotting. However, surface biotinylation of the cells followed by avidin pull-down showed that the A(2A) receptor at the cell membrane was increased after anoxia. This was supported by immunolabelling of the A(2A) receptors: much of the receptor protein was present in the cytoplasm of normoxic cells, but in cells subjected to anoxia the A(2A) receptor immunolabelling at the cell membrane was more pronounced, indicating redistribution of the receptors from intracellular pools to the cell membrane during anoxia.