ASSOCIATION OF GUINEA-PIG LUNG BOMBESIN RECEPTORS WITH PERTUSSIS-TOXIN-SENSITIVE GUANINE-NUCLEOTIDE-BINDING PROTEINS

The possible interaction of bombesin receptors with guanine nucleotide binding protein in guinea pig lung was studied. The non-hydrolysable GTP analogue guanosine-5'-[gamma-thio]triphosphate (GTP gamma S) was s hown to decrease [I-125-Tyr(4)]bombesin binding in a concentration-dep endent manner. The specificity of this effect was assessed by examinin g the effects of other guanine nucleotides on this binding at a concen tration of 1 mM. GMP and GDP weakly inhibited [I-125-Tyr(4)]bombesin b inding (2 and 19%, respectively), whereas GTP, guanosine-5'-[beta-thio ]triphosphate (GDP beta S), and 5-guanylylimidodiphosphate (GppNHp) ex hibited similar potencies, inducing 52%, 46%, and 43% inhibition of [I -125-Tyr(4)]bombesin binding respectively. Saturation experiments perf ormed in the absence and presence of 100 mu M GTP gamma S indicated th e presence of a single population of receptors in both cases. However, the addition of GTP gamma S induced a marked decrease in the number o f receptors (from 1.76 fmol/mg protein to 0.78 fmol/mg protein) withou t significantly altering the dissociation constant (K-d) These results provide evidence that bombesin receptors are coupled to a G-protein s ignal transduction pathway in guinea pig lung. We have further charact erised this G-protein on the basis of its toxin sensitivity. Pretreatm ent of the lung membranes with either pertussis (10 mu g/ml) or choler a toxin (50 mu g/ml) was performed. Cholera toxin treatment did not af fect the ability of GTP gamma S to inhibit [I-125-Tyr(4)]bombesin bind ing to guinea pig lung membranes. However, pertussis toxin treatment i nduced a decrease in binding and resulted in the inability of GTP gamm a S to inhibit [I-125-Tyr(4)]bombesin binding in a concentration-depen dent manner. These results suggest that bombesin receptors of the guin ea pig lung interact with pertussis toxin-sensitive G-proteins.