Spermine and spermidine, modulators of the cell surface enzyme adenylate cyclase

Adenylate cyclase activity was measured in membrane preparations of cultured fibroblasts from controls and patients with cystic fibrosis. Enzyme activity increased as the transition from exponential growth to confluence occurred; sodium fluoride-stimulated activity more markedly displayed this relationship than basal cyclase activity. The in vitro addition of spermine (1 X 10(-6) to 2 X 10(-3) M) to membrane preparations caused inhibition of basal and sodium fluoride-stimulated enzyme activity, with 50% inhibition of basal activity occurring at 10(-6) M spermine. Spermidine (10(-4) M) caused 15--25% inhibition of adenylate cyclase activity. The increase in fibroblast adenylate cyclase activity during the transition from exponential growth was comparable in cells obtained from cystic fibrosis patients and control subjects. Basal and sodium-fluoride stimulated adenylate cyclase activity as well as inhibition of this enzyme activity by spermidine and spermine were undistinguishable between the different cell genotypes. A potential modulation of cellular proliferative activity through polyamine interaction with the adenylate cyclase system is postulated.