Adenylyl cyclase in lung from hypersensitive guinea pig displays increased responsiveness to guanine nucleotides and isoprenaline: The role of the G proteins Gs and Gi

Basal adenylyl cyclase activity in lung membranes isolated from hypersensitive guinea pigs was increased and more sensitive to stimulation by isoprenaline, GTP and GppNHp when compared to adenylyl cyclase in lung membranes isolated from normal healthy guinea pigs. Maximal forskolin-stimulated adenylyl cyclase activity was unaltered. There was no change in the immunological quantitative amounts of either alpha subunits of the G proteins G(iII) and G(s) (G(o), G(iI) and G(iIII) were not present). Maximal pertussis-toxin- and cholera-toxin-catalyzed ADP-ribosylation of G(ialpha) and G(salpha) respectively were not significantly altered. The addition of purified protein kinase C to isolated lung membranes resulted in the phosphorylation of the alpha subunit of G(s) (stoichiometry was 0.53 mol of P-32 incorporated/mol of G(salpha)). Addition of protein kinase C to lung membranes isolated from hypersensitive guinea pigs was equally effective at catalysing the phosphorylation of the alpha subunit of G(s). GppNHp-stimulated and basal adenylyl cyclase activity was also enhanced in isolated tracheal smooth-muscle membranes from hypersensitive guinea pigs. These results suggest that hypersensitive reactions are associated with the improved coupling of the stimulatory G protein (G(s)) with adenylyl cyclase.