INHIBITION OF PERTUSSIS TOXIN CATALYZED ADP-RIBOSYLATION OF G-PROTEINS BY MEMBRANE DEPOLARIZATION IN RAT-BRAIN SYNAPTONEUROSOMES

Rat brainstem synaptoneurosomes at resting and depolarization potentials were subjected to ADP-ribosylation in the presence of pertussis toxin (PTX). Subsequent [P-32]ADP-ribosylation of synaptoneurosomal membranes revealed labeling of a 39-kDa protein band which reacted with antibodies to the alpha-subunit of G-proteins, mainly G(o). ADP-ribosylation of the G-proteins was completely achieved in synaptoneurosomes at resting potential ([K+] = 4.7 mM). In the depolarized synaptoneurosomes, however, the higher the membrane potential the lower the extent of ADP-ribosylation achieved (46% and 11% in K+ concentrations of 50 and 100 mM, respectively). A similar effect of membrane depolarization on PTX-catalyzed ADP-ribosylation was expressed in the functional coupling between G-protein activation and changes induced in the muscarinic receptor affinity. These findings may indicate a depolarization-induced inhibition of PTX-catalyzed ADP-ribosylation of G-proteins.