Binding characterization of cholecystokinin receptors in rat pulmonary interstitial macrophages / 中国病理生理杂志

ABSTRACT

AIM: To investigate the binding characteristics of cholecystokinin receptors in rat pulmonary interstitial macrophages (PIMs). METHODS: The PIMs were isolated from rat lung tissues, purified using the collagenase digestion method combined with alveolar lavage and pulmonary vessel perfusion. The PIM membrane was obtained by supercentrifuge. Receptors for CCK in PIMs were examined using [~3H] labeled CCK-8S as ligand. The specificity of [~3H]-CCK-8S binding to PIMs membrane and the subtypes of CCK receptors were determined by competitive inhibition experiments with CCK-8S, CCK-A and CCK-B receptors selective antagonists (CR1409 and CR2945). The effects of time and incubation temperature on the specific binding were also observed. RESULTS: The specific binding of [~3H]-CCK-8S was not detected in normal rat PIMs, but was detected in the rat administrated with LPS for 48 h. The capacity of ligand-receptor binding was dependent on the incubation temperature and time. Scatchard analysis of the saturation curves suggested that the presence of CCK receptors with high affinity [Kd=(0.68?0.28)mmol/L] and low binding capacity [Bmax=(32.50?2.70) pmol?g~(-1) protein] in PIMs. By means of competitive inhibition studies, the specific binding of [~3H]-CCK-8S to rat PIMs was inhibited by unlabelled CCK-8S [IC_(50)=(3.20?1.13) nmol/L], CCK-AR specific antagonist CR 1 409 [IC_(50)=(0.19?0.06)?mol/L] and CCK-BR specific antagonist CR 2945[IC_(50)=(2.30?0.80)nmol/L]. CONCLUSION: These results suggest the presence of two subtypes of CCK-AR and CCK-BR and provide a structural basis for CCK to play a pivotal role in PIMs.