Forskolin inhibition of cyclic AMP generation in J774 macrophages

Abstract

Forskolin inhibited cyclic AMP generation in J774 macrophage cells in response to isoproterenol. Forskolin, 10 nM-0.1 mM, also inhibited the adenylate cyclase activity of membrane preparations. The basal activity and the isoproterenol-, cholera toxin-, fluoride- or GppNHp-stimulated activities were maximally depressed by 10 μM forskolin (30–70% inhibition, EC 50 = 0.3–0.5 μM). This effect was achieved similarly in membranes from pertussis toxin-treated cells. Forskolin required guanine nucleotides for inhibition. In the absence of GTP the decrease in basal activity was reversed into stimulation (EC 50 = 10 μM forskolin). Reversal of inhibition into activation also followed the addition of 1 mM MnCl 2 (EC 50 = 10 μM forskolin). 1,9-Dideoxyforskolin was ineffective to alter adenylate cyclase activity. In contrast, a water-soluble derivative of forskolin was as active as forskolin to regulate activity. The results suggest that forskolin may interact with adenylate cyclase to cause either activation or inhibition depending on the degree of activation of N s and on its interaction with the catalyst.