High-affinity receptors for bombesin-like peptides in normal guinea pig lung membranes.

The binding of the radiolabelled bombesin analogue 125I-Tyr4]bombesin to guinea-pig lung membranes was investigated. Binding of 125I-Tyr4]bombesin was specific, saturable, reversible and linearly related to the protein concentration. Scatchard analysis of equilibrium binding data at 25 degrees C indicated the presence of a single class of non-interacting binding sites for bombesin (Bmax = 7.7 fmol/mg protein). The value of the equilibrium dissociation constant (KD = 90 pM) agrees with a high-affinity binding site. Bombesin and structurally related peptides such as Tyr4]bombesin, neuromedin B and neuromedin C inhibited the binding of 125I-Tyr4]bombesin in an order of potencies as follows: Tyr4]bombesin greater than bombesin greater than or equal to neuromedin C much greater than neuromedin B. These results indicate that guinea-pig lung membranes possess a single class of bombesin receptors with a high affinity for bombesin and a lower one for neuromedin B.