Antipsychotic drugs of known antidiarrhoeal and anticalmodulin activity inhibited the cholera-toxin-catalysed ADP-ribosylation of proteins of M r, 37000,40000 and 45000 (thought to be regulatory components of the adenylate cyclase complex) that was previously shown to occur in plasma membranes from rabbit intestinal epithelial cells [(1989) Biochim. Biophys. Acta 1014, 289-297]. There was no obvious correlation between the different activities of the drugs. The drugs also inhibited adenylate cyclase activity, but in this case the inhibition correlated well with the known IC50 values of the drugs for anticalmodulin activity and with their antidiarrhoeal activities.
