[Cholecystokinin receptors on guinea pig gastric chief cell membranes]

Cholecystokinin (CCK) binding to its receptors on guinea pig gastric chief cell membranes was characterized with 125I-COOH terminal octapeptide of CCK (125I-CCK8). Specific binding of 125I-CCK8 to chief cell membranes was maximal at pH 6.0 and 30 degrees C after 180 min of incubation and reversible upon the addition of 10(-7) M unlabeled CCK8. CCK analogs such as CCK8, gastrin-I, and COOH-terminal tetrapeptide of CCK (CCK4) competitively inhibited the labeled CCK8 binding with the half maximal inhibitory concentration of 10(-10) M, 3 X 10(-7) M and 10(-6) M, respectively. Furthermore, guanine nucleotide analogs such as GTP gamma S and Gpp(NH)p also inhibited the labeled CCK8 binding to chief cell membranes. Scatchard analysis of the binding data at pH 6.0 revealed two orders of the binding sites and GTP gamma S decreased the binding by converting two binding sites of the receptors to only one site of lower affinity. These results suggest that there are specific receptors for CCK, which are coupled to a guanine nucleotide regulatory protein on guiea pig gastric chief cell membranes.