RMI 12330 A, an inhibitor of adenylate cyclase in rat liver.

RMI 12330 A, (N,-(cis-2-phenylcyclopentyl) azacyclotridecan-2-imine hydrochloride), has been reported to inhibit choleratoxin-induced intestinal hypersecretion, presumably via an inhibition of mucosal adenylate cyclase (ATP:pyrophosphate-lyase (cyclizing), EC 4.6.1.1). We report here that the adenylate cyclase activity of a rat liver plasma membrane preparation was inhibited by concentrations of RMI 12330 A ranging from 10 muM to 5mM. Similar effects were observed when the adenylate cyclase preparation was assayed in the presence of 10 mM NaF, 0.1 muM glucagon or 1 muM (--)-epinephrine plus 10 muM GTP. The effect of RMI 12330 A was not due to the inhibition of the regenerating system present in the incubation medium, since the effect was preserved in its absence. The inhibition brought about by RMI 12330 A was due to a decrease in the maximal velocity of the reaction; the affinity of the enzyme for the substrate remained unmodified. The inhibition was immediate and irreversible, even after several washes of the membranes previously preincubated with the drug. Complete inhibition of cyclase was obtained at a concentration of 370 nmol of RMI 12330 A per mg of membrane protein. The drug acted with a similar dose-response curve upon intact as well as detergent-dispersed cyclase preparations.