Lithium does not alter ADP-ribosylation of Gi/Go catalyzed by pertussis toxin in rat brain.

The influences of lithium in vitro and ex vivo on the ADP-ribosylation of Gi/Go catalyzed by pertussis toxin (islet-activating protein, IAP) were investigated in cerebral cortical and hippocampal membranes from rats. Incorporation of [32P]ADP-ribose into 40-41 kDa band catalyzed by IAP was markedly reduced by the addition of non-hydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) or guanosine 5'-(beta, gamma-imido)triphosphate [Gpp(NH)p], in the presence of MgCl2 but not in the absence of MgCl2. The amounts of IAP-catalyzed ADP-ribosylation of Gi/Go in the presence of 100 microM guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) and 50 mM EDTA and in the absence of MgCl2 were in proportion to the protein contents between 30 and 60 micrograms/tube, suggesting that the determination of [32P]ADP-ribosylation could be used quantitatively within this limited range. Addition of LiCl in vitro did not affect the IAP-mediated ADP-ribosylation of Gi/Go up to the concentration of 5 mM. The values of ADP-ribosylation of Gi/Go in the presence of 100 microM GTP gamma S were reduced by MgCl2 concentration-dependently. However, this inhibitory effect of MgCl2 was not influenced by 2 mM LiCl in vitro. Furthermore, chronic treatment with a diet containing 0.2% lithium carbonate did not alter the [32P]ADP-ribosylation of Gi/Go catalyzed by IAP.