Detection of multiple H3 receptor affinity states utilizing [3H]A-349821, a novel, selective, non-imidazole histamine H3 receptor inverse agonist radioligand.
1. A-349821 is a selective histamine H3 receptor antagonist/inverse agonist. Herein, binding of the novel non-imidazole H3 receptor radioligand [3H]A-349821 to membranes expressing native or recombinant H3 receptors from rat or human sources was characterized and compared with the binding of the agonist [3H]N--methylhistamine ([3H]NMH). 2. [3H]A-349821 bound with high affinity and specificity to an apparent single class of saturable sites and recognized human H3 receptors with 10-fold higher affinity compared to rat H3 receptors. [3H]A-349821 detected larger populations of receptors compared to [3H]NMH. 3. Displacement of [3H]A-349821 binding by H3 receptor antagonists/inverse agonists was monophasic, suggesting recognition of a single binding site, while that of H3 receptor agonists was biphasic, suggesting recognition of both high- and low-affinity H3 receptor sites. 4. pKi values of high-affinity binding sites for H3 receptor competitors utilizing [3H]A-349821 were highly correlated with pKi values obtained with [3H]NalphaMH, consistent with labelling of H3 receptors by [3H]A-349821. 5. Unlike assays utilizing [3H]NMH, addition of GDP had no effect on saturation parameters measured with [3H]A-349821, while displacement of [3H]A-349821 binding by the H3 receptor agonist histamine was sensitive to GDP. 6. In conclusion, [3H]A-349821 labels interconvertible high- and low-affinity states of the H3 receptor, and displays improved selectivity over imidazole-containing H3 receptor antagonist radioligands. [3H]A-349821 competition studies showed significant differences in the proportions and potencies of high- and low-affinity sites across species, providing new information about the fundamental pharmacological nature of H3 receptors.
Witte
David G
DG
Neuroscience Research, Dept. R4MN, Global Pharmaceutical Research Division, Abbott Laboratories, Bldg. AP9A-2, 100 Abbott Park Road, Abbott Park, IL 60064, USA. david.g.witte@abbott.com
Yao
Betty Bei
BB
Miller
Thomas R
TR
Carr
Tracy L
TL
Cassar
Steven
S
Sharma
Rahul
R
Faghih
Ramin
R
Surber
Bruce W
BW
Esbenshade
Timothy A
TA
Hancock
Arthur A
AA
Krueger
Kathleen M
KM
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001713:Biphenyl Compounds / Q000493:pharmacokinetics*; D002478:Cells, Cultured; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D017442:Histamine Agonists / Q000494:pharmacology; D006633:Histamine Antagonists / Q000494:pharmacology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008761:Methylhistamines / Q000494:pharmacology; D008954:Models, Biological; D011485:Protein Binding / Q000187:drug effects; D011869:Radioligand Assay / Q000379:methods*; D051381:Rats; D018100:Receptors, Histamine H3 / Q000737:chemistry* / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
C489829:A349821; D001713:Biphenyl Compounds; D017442:Histamine Agonists; D006633:Histamine Antagonists; D007093:Imidazoles; D008761:Methylhistamines; D018100:Receptors, Histamine H3; D006153:Guanosine Diphosphate; D006632:Histamine; D013890:Thiourea; C086108:clobenpropit; C048140:N-methylhistamine