Characterization of the binding of [3H]-clobenpropit to histamine H3-receptors in guinea-pig cerebral cortex membranes.
1 We have investigated the binding of a novel histamine H3-receptor antagonist radioligand, [3H]- clobenpropit ([3H]-VUF9153), to guinea-pig cerebral cortex membranes. 2 Saturation isotherms for [3H]-clobenpropit appeared biphasic. Scatchard plots were curvilinear and Hill plot slopes were significantly less than unity (0.63+/-0.03; n = 12+/-s.e.mean). The radioligand appeared to label two sites in guinea-pig cerebral cortex membranes with apparent affinities (pKD') of 10.91+/-0.12 (Bmax = 5.34+/-0.85 fmol mg(-1) original wet weight) and 9.17+/-0.16 (Bmax = 23.20+/-6.70 fmol mg(-1)). 3 In the presence of metyrapone (3 mM) or sodium chloride (100 mM), [3H]-clobenpropit appeared to label a homogeneous receptor population (Bmax=3.41+/-0.46 fmol mg-1 and 3.49+/-0.44 fmol mg(-1), pKD' = 10.59+/-0.17 and 10.77+/-0.02, respectively). Scatchard plots were linear and Hill slopes were not significantly different from unity (0.91+/-0.04 and 0.99+/-0.02, respectively). Granisetron (1 microM), rilmenidine (3 microM), idazoxan (0.3 microM), pentazocine (3 microM) and 1,3-di-(2-tolyl)guanidine (0.3 microM) had no effect on the binding of [3H]-clobenpropit. 4 The specific binding of [3H]-clobenpropit appeared to reach equilibrium after 25 min at 21+/-3 degrees C and remained constant for >180 min. The estimated pKD' (10.27+/-0.27; n = 3+/-s.e.mean) was not significantly different from that estimated by saturation analysis in the presence of metyrapone. 5 A series of histamine H3-receptor ligands expressed affinity values for sites labelled with [3H]-clobenpropit which were not significantly different from those estimated when [3H]-R-alpha-MH was used to label histamine H3-receptors in guinea-pig cerebral cortex membranes.
Harper
E A
EA
James Black Foundation, 68 Half Moon Lane, Dulwich, London SE24 9JE.
Shankley
N P
NP
Black
J W
JW
D000818:Animals; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000378:metabolism*; D006168:Guinea Pigs; D006633:Histamine Antagonists / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008797:Metyrapone / Q000378:metabolism; D010880:Piperidines / Q000378:metabolism; D011869:Radioligand Assay; D018100:Receptors, Histamine H3 / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000378:metabolism; D014316:Tritium
C103528:GR 168320; D006633:Histamine Antagonists; D007093:Imidazoles; D010880:Piperidines; D018100:Receptors, Histamine H3; D014316:Tritium; D013890:Thiourea; C052075:thioperamide; C086108:clobenpropit; D008797:Metyrapone