Ea. Harper et al., Characterization of the binding of [H-3]-clobenpropit to histamine H-3-receptors in guinea-pig cerebral cortex membranes, BR J PHARM, 128(4), 1999, pp. 881-890
1 We have investigated the binding of a novel histamine H-3-receptor antago
nist radioligand, [H-3]-clobenpropit ([H-3]-VUF9153), to guinea-pig cerebra
l cortex membranes.
2 Saturation isotherms for [H-3]-clobenpropit appeared biphasic. Scatchard
plots were curvilinear and Hill plot slopes were significantly less than un
ity (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
(pK(D)') of 10.91 +/- 0.12 (B-max = 5.34 +/- 0.85 fmol mg(-1) original wet
weight) and 9.17 +/- 0.16 (B-max = 23.20 +/- 6.70 fmol mg(-1)).
3 In the presence of metyrapone (3 mM) or sodium chloride (100 mM), [H-3]-c
lobenpropit appeared to label a homogeneous receptor population (B-max = 3.
41 +/- 0.46 fmol mg(-1) and 3.49 +/- 0.44 fmol mg(-1), pK(D)' = 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 mu M), rilmenidine (3 mu M), idazo
xan (0.3 mu M), pentazocine (3 mu M) and 1,3-di-(2-tolyl)guanidine (0.3 mu
M) had no effect on the binding of [H-3]-clobenpropit.
4 The specific binding of [H-3]-clobenpropit appeared to reach equilibrium
after 25 min at 21 +/- 3 degrees C and remained constant for > 180 min. The
estimated pK(D)' (10.27 +/- 0.27; n = 3 +/- s.e.mean) was not significantl
y different from that estimated by saturation analysis in the presence of m
etyrapone.
5 A series of histamine H-3-receptor ligands expressed affinity values for
sites labelled with [H-3]-clobenpropit which were not significantly differe
nt from those estimated when [H-3]-R-alpha-MH was used to label histamine H
-3-receptors in guinea-pig cerebral cortex membranes.