Characterization of Vasoactive Intestinal Peptide (VIP) receptors in mammalian lung

125I-VIP bound specifically to sites on human, rat, guinea pig, and rabbit lung membranes with a dissociation constant (K D) of 60–200 pM and binding site maxima of 200–800 fmol/mg of protein. The presence of a second lower affinity site was detected but not investigated further. High affinity 125I-VIP binding was reversible and displaced by structurally related peptides with an order of potency: VIP > rGRF > PHI > hGRF > secretin=Ac Tyr 1 D Phe 2 GRF. 125I-VIP has been covalently incorporated into lung membranes using disuccinimidyl suberate. Sodium dodecyl sulfate-polyacrilamide gel electrophoresis of labeled human, rat, and rabbit lung membranes revealed major 125I-VIP-receptor complexes of: Mr=65,000 , 56,000, and 64,000 daltons, respectively. Guinea pig lung membranes exhibited two 125I-VIP-receptor complexes of Mr=66,000 and 60,000 daltons. This labeling pattern probably reflects the presence of differentially glycosylated forms of the same receptor since treatment with neuroaminidase resulted in a single homogeneous band ( Mr=57,000 daltons ). Soluble covalently labeled VIP receptors from guinea pig and human lung bound to and were specifically eluted from agarose-linked wheat germ agglutinin columns. Our studies indicate that mammalian lung VIP receptors are glycoproteins containing terminal sialic acid residues.