Ea. Harper et al., Characterization of the binding of a novel radioligand to CCKB/gastrin receptors in membranes from rat cerebral cortex, BR J PHARM, 126(6), 1999, pp. 1504-1512
1 We have investigated the binding of a novel radiolabelled CCKB/gastrin re
ceptor ligand, [H-3]-JB93182 (5[[[(1S)-[[3, 5-dicarboxyphenyl)amino]carbony
l]-2-phenylethylamino]-carbonyl]-6-[[(1-adamantylmethyl) amino]carbonyl]-in
dole), to sites in rat cortex membranes,
2 The [H-3]-JB93182 was 97% radiochemically pure as assessed by reverse-pha
se HPLC (RP-HPLC) and was not degraded by incubation (15 min) wit-h rat cor
tex membranes.
3 Saturation analysis indicated that [H-3]-JB93182 labelled a homogeneous p
opulation of receptors in rat cortex membranes (pK(D) = 9.48 +/- 0.08, B-ma
x = 3.61 +/- 0.65 pmol g(-1) tissue, n(H) = 0.97 +/- 0.02, n = 5). The pK(D
) was not significantly different when estimated by association-dissociatio
n analysis (pK(D) = 9.73 +/- 0.11; n = 10).
4 In competition studies, the low affinity of the CCKA receptor antagonists
, L-364,718; SR27897 and 2-NAP, suggest that, under the assay conditions em
ployed, [H-3]-JB93182 (0.3 nM) does not label CCKA receptors in the fat cor
tex.
5 The affinity estimates obtained for reference CCKB/gastrin receptor antag
onists were indistinguishable from one of the affinity values obtained when
a two site model was used to interpret [I-125]-BH-CCK8S competition curves
obtained in the same tissue (Harper et al,, 1999).
6 This study provides further evidence for the existence of two CCK(B/)gast
rin sites in rat cortex. [H-3]-JB93182 appears to label selectively sites p
reviously designated as gastrin-G(1) and therefore it may be a useful compo
und for thefurther discrimination and characterization of these putative re
ceptor subtypes.