Treatment of intact striatal neurones with cholera toxin or 8‐bromoadenosine 3′,5′‐(cyclic)phosphate decreases the ability of pertussis toxin to ADP‐ribosylate the α‐subunits of inhibitory and other guanine‐nucleotide‐binding regulatory proteins, G i and G o

Using primary cultures of striatal neurones from the mouse embryo, we showed that treatment of intact cells with cholera toxin (5 μg/ml, 22 h) decreases the subsequent ADP‐ribosylation of the α subunit of the guaninenucleotide‐binding regulatory protein G o (G o α) and the α subunit of the inhibitory guanine‐nucleotide‐binding regulatory protein (G i α) of adenylate cyclase, which is catalyzed in vitro on neuronal membranes by pertussis toxin. The inhibitory effect of cholera toxin could not only be attributed to an increased production of cAMP in neurones. Treatment of cells with 0.1 μM 8‐bromoadenosine 3′,5′‐(cyclic)phosphate (Br 8 cAMP) for 16 h, or with 0.1 mM Br 8 cAMP for 5 min, mimicked the effect of cholera toxin on the ADP‐ribosylation of G o α and G i α in vitro . However, the two agents seem to act through distinct mechanisms. The protein kinase inhibitor 1‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine prevented the action of Br 8 cAMP but not that of cholera toxin. In addition, measurements of the p I of the G o α, deduced from immunoblots of two‐dimensional gels performed using a specific antibody directed against G o α, suggest that treatment of neurones with cholera toxin induces ADP‐ribosylation of G o α in intact cells, while Br 8 cAMP does not.