Forskolin stabilizes a functionally coupled state between activated guanine nucleotide-binding stimulatory regulatory protein, N_s, and catalytic protein of adenylate cyclase system in rat erythrocytes

Guanine nucleotide-binding stimulatory regulatory protein of adenylate cyclase system, N_s, in rat erythrocytes was activated by the treatment with guanylyl 5′-imidodiphosphate or NaFAlCl₃ in the presence of Mg²⁺. The activation was counterbalanced to the basal state either by the removal of Mg²⁺ or by the addition of β(γ)-subunit of N protein of this system. The depression from the activated state was markedly protected by the coexistence of forskolin at the time of the deactivation depending on the dose of forskolin. EC₅₀ of forskolin for the stabilizing effect was much lower than that for the stimulation of adenylate cyclase activity. These data indicate that forskolin has an effect on the interaction between N_s and catalytic unit of adenylate cyclase system in addition to the direct effect on the catalytic unit.