Characterization of specific binding sites for vasoactive intestinal peptide in rat intestinal epithelial cell...

Specific binding sites for vasoactive intestinal peptide were characterized in plasma membranes from rat intestinal epithelial cells. At 30 degrees C, the interaction of 125I-labelled peptide with intestinal membranes was rapid, reversible, specific and saturable. At equilibrium, the binding of 125I-labelled peptide was competitively inhibted by native peptide in the 3 . 10(-11)--3 . 10-(7) M range concentration. Scatchard analysis of binding data suggested the presence of two distinct classes of vasoactive intestinal peptide binding sites: a class with a high affinity (Kd = 0.28 nM) and a low capacity (0.8 pmol peptide/mg membrane protein) and a class with a low affininty (Kd = 152 nM) and a high capacity (161 pmol peptide/mg membrane protein). Secretin competitively inhibited binding of 125I-labelled peptide but its potency was 1/1000 that of native peptide. Glucagon and the gastric inhibitory peptide were ineffective. The guanine nucleotides, GTP and Gpp(NH)p inhibited markedly the interaction of 125I-labelled peptide with its binding sites, by increasing the rate of dissociation of peptide bound to membranes. The other nucleotides triphosphate tested (ATP, ITP, UTP, CTP) were also effective in inhibiting binding of 125I-labelled peptide to membranes but their potencies were 1/100--1/1000 that of guanine nucleotides. The specificity and affinity of the vasoactive intestinal peptide-binding sites in plasma membranes prepared from rat intestinal epithelial cells, which is in agreement with an adenylate cyclase highly sensitive to the peptide recently characterized in these membranes (Amiranoff, B., Laburthe, M., Dupont, C. and Rosselin, G. (1978) Biochim. Biophys. Acta 544, 474--481) further argue for a physiological role of the peptide in the regulation of intestinal epithelial function.