ADENOSINE RECEPTOR-INDUCED CAMP CHANGES IN D384 ASTROCYTOMA-CELLS AND THE EFFECT OF BRADYKININ THEREON

In human D384 astrocytoma cells, cyclic AMP accumulation can be conveniently studied after labelling of die adenosine triphosphate pool (15 fmol cell-1) with [H-3]adenine. In this study, adenosine had a biphasic effect on cyclic AMP accumulation, which was scarcely altered by blocking adenosine uptake and metabolism. Low concentrations of adenosine led to an inhibition of cyclic AMP accumulation, and higher concentrations led to stimulation. No effect of adenosine on cyclic AMP was observed unless phosphodiesterase was inhibited by rolipram. The A1 receptor antagonist DPCPX attenuated the inhibitory phase of adenosine response, and enhanced the cyclic AMP accumulation induced by adenosine analogues. The cyclic AMP accumulation was stimulated by NECA > ADO > CGS 21680 > CV 1808 > CPA greater-than-or-equal-to CHA, indicating mediation by A2 receptors. The stimulatory effect of NECA was much more effectively blocked by the combined A1 and A2 receptor antagonist CGS 15943 (K(B) 4 nmol l-1) than by the A1 antagonist DPCPX (K(B) 110 nmol l-1). Treatment of the cells with pertussis toxin (0.2-mu-g ml-1 for 2.5 h) potentiated the cyclic AMP response to adenosine analogues significantly. The cyclic AMP response to NECA was enhanced by the protein kinase C activator phorbol dibutyrate even after pertussis toxin treatment. By contrast, nanomolar concentrations of bradykinin, which increases Ca2+-levels and protein kinase C activity in D384 cells, reduced NECA-induced cyclic AMP accumulation in control and pertussis toxin-treated cells. Thus, D384 cells possess both A1 and A2 adenosine receptors influencing cyclic AMP in opposite directions. A2 receptor-mediated cyclic AMP accumulation can be stimulated by activating protein kinase C and inhibited by raising Ca2+. Neither the effects of protein kinase C activation nor those of bradykinin required pertussis toxin-sensitive G-proteins.