HIGH-AFFINITY RECEPTORS FOR BOMBESIN-LIKE PEPTIDES IN NORMAL GUINEA-PIG LUNG MEMBRANES

The binding of the radiolabelled bombesin analogue [I-125-Tyr4]bombesin to guinea-pig lung membranes was investigated. Binding of [I-125-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 (B(max) = 7.7 fmol/mg protein). The value of the equilibrium dissociation constant (K(D) = 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 [I-125]-Tyr4]bombesin in an order of potencies as follows: [Tyr4]bombesin > bombesin greater-than-or-equal-to neuromedin C >> 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.