Characterization of a vasoactive intestinal peptide-sensitive adenylate cyclase in rat intestinal epithelial cell membranes

A vasoactive intestinal peptide-sensitive adenylate cyclase in intestinal epithelial cell membranes was characterized. Stimulation of adenylate cyclase activity was a function of vasoactive intestinal peptide concentration over a range of 1 · 10⁻¹⁰−1 · 10⁻⁷ M and was increased six-times by a maximally stimulating concentration of vasoactive intestinal peptide. Half-maximal stimulation was observed with 4.1 ± 0.7 nM vasoactive intestinal peptide. Fluoride ion stimulated adenylate cyclase activity to a higher extent than did vasoactive intestinal peptide. Under standard assay conditions, basal, vasoactive inteetinal peptide- and fluoride-stimulated adenylate cyclase activities were proportional to time of incubation up to 15 min and to membrane concentration up to 60 μg protein per assay. The vasoactive intestinal peptide-sensitive enzyme required 5–10 mM Mg²⁺ and was inhibited by 1 · 10⁻⁵ M Ca²⁺. At sufficiently high concentrations, both ATP (3 mM) and Mg²⁺ (40 mM) inhibited the enzyme.Secretin also stimulated the adenylate cyclase activity from intestinal epithelial cell membranes but its effectiveness was 1/1000 that of vasoactive intestinal peptide. Prostaglandins E₁ and E₂ at 1 · 10⁻⁵ M induced a two-fold increase of cyclic AMP production. Vasoactive intestinal peptide was the most potent stimulator of adenylate cyclase activity, suggesting an important physiological role of this peptide in the cyclic AMP-dependent regulation of the intestinal epithelial cell function.