Characterization of receptors for glucagon‐like peptide‐1(7–36) amide on rat lung membranes

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Abstract
Specific binding of 125I‐labelled GLP‐1(7–36)amide to rat lung membranes was dependent upon time and temperature and was proportional to membrane protein concentration. Binding was inhibited in a concentration‐dependent manner by unlabelled GLP‐l(7–36)amide consistent with the presence of a single class of binding sites with a dissociation constant (K d) of 1.67 ± 0.29 . GLP‐1(1–36)amide was 260 times less potent in inhibiting the binding of 125I‐labelled GLP‐1(7 36)amide to lung membranes (k d of 448 ± 93 ). Vasoactive intestinal polypeptide and peptide‐histidine‐isolcucine also displaced 125I‐labelled GLP‐1(7–36)amide from the receptor concentration‐dependently; the k d was 4.31 ± 0.8 and 7.93 ± 4.79 . respectively. Guaninc nucleotides (GTP‐γ‐S, GDP‐β‐S) decreased the binding of 125I‐labelled GLP‐1(7–36)amide to rat lung membranes as was found for GLP‐1(7–36)amide receptors in RINm5F cells which were also shown to be coupled to the adenylate cyclase system.