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Analysis of variation in L‐365,260 competition curves in radioligand binding assays
Author(s) -
Harper E.A.,
Roberts S.P.,
Shankley N.P.,
Black J.W.
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15597.x
Subject(s) - radioligand , guinea pig , medicine , receptor , cortex (anatomy) , chemistry , cholecystokinin , endocrinology , population , binding site , radioligand assay , biology , microbiology and biotechnology , biochemistry , neuroscience , environmental health
1 . For several years, we have used the cholecystokinin (CCK) B /gastrin receptor selective antagonist, L‐365,260, as a reference compound in a variety of studies in CCK B /gastrin receptor radioligand binding assays. Here, we have analysed the competition curve data sets obtained between L‐365,260 and [ 125 I]‐BH‐CCK8S in guinea‐pig gastric gland and mouse and rat cerebral cortex preparations. 2 . Competition curves obtained for L‐365,260 in the mouse cortex assay were not different from rectangular hyperbolae (slope = 1.01 ± 0.02) implying the presence of a single population of binding sites (p K I = 8.41 ± 0.01; data from 47 experiments, slope constrained to unity). However, in the rat cortex and guinea‐pig gastric gland assays, the mean slope of the competition curves was significantly less than one and the mean apparent p K I significantly lower than that obtained in the mouse cortex (slope = 0.85 ± 0.03, 0.90 ± 0.03; apparent p K I = 7.98 ± 0.05, 8.07 ± 0.05; 48 and 45 experiments, in rat and guinea‐pig, respectively). The distribution of the individual p K 1 and slope estimates of the competition curves in these two assays was consistent with expectations for the variable expression (in terms of absolute number and proportion) of two binding sites. The two sites were characterized by p K 1 values for L‐365,260 of 8.50 ± 0.04 and 8.48 ± 0.04 for the high affinity site and 7.32 ± 0.04 and 7.22 ± 0.06 for the low affinity site in guinea‐pig and rat, respectively. 3 . The affinity estimates for L‐365,260, although obtained on different tissues, are consistent with data obtained from the analysis of L‐365,260 antagonism of pentagastrin‐stimulated responses in mouse and rat stomach (acid secretion) and guinea‐pig gastric muscle (isotonic contraction) assays. To this extent, these data suggest the existence of two CCK B /gastrin receptor subtypes.