Article date: October 1994
By: F.P. Jansen, T.S. Wu, H.‐P. Voss, H.W.M. Steinbusch, R.C. Vollinga, B. Rademaker, A. Bast, H. Timmerman, in Volume 113, Issue 2, pages 355-362
The binding of the first selective radiolabeled histamine H3‐receptor antagonist [125I]‐iodophenpropit to rat cerebral cortex membranes was characterized.
[125I]‐iodophenpropit, radiolabeled to a high specific activity of 1900 Ci mmol‐1, saturably bound to a single class of sites with a KD of 0.57 ± 0.16 nm (n = 4) and Bmax of 268 ± 119 fmol mg‐1 protein.
Specific binding at a concentration below 1 nm represented 50 to 60% of total binding.
Binding of [125I]‐iodophenpropit to rat cerebral cortex membranes was readily displaced by histamine H3‐agonists and antagonists. In contrast, the inhibitory potencies of selective histamine H1‐ and H2‐receptor ligands were very low.
[125]‐iodophenpropit was biphasically displaced by the histamine H3‐receptor antagonists, burimamide and dimaprit, which may indicate the existence of histamine H3‐receptor subtypes. Other histamine H3‐receptor antagonists showed a monophasic displacement.
Competition binding curves of H3‐agonists were biphasic and showed a rightward shift upon the addition of the nonhydrolysable GTP analogue, guanosine 5′‐o‐(3‐thio) triphosphate (GTPγS; 100 μm) which implicates the interaction of histamine H3‐receptors with G‐proteins. The affinities of the H3‐receptor antagonists iodophenpropit, thioperamide and burimamide were not altered by GTPγS.
Histamine competition binding curves were shifted to the right by different nucleotides (100 μm) with a rank order of potency GTPγS > Gpp(NH)p, GTP.
In vitro autoradiographic studies revealed a heterogeneous distribution of [125I]‐iodophenpropit binding sites in rat brain, with highest densities observed in specific cerebral cortical areas and layers, the caudate‐putamen complex, the olfactory tubercles, the hippocampal formation, the amygdala complex, the hypothalamic area and the mammillary bodies.
It is concluded that the histamine H3‐receptor antagonist, [125I]‐iodophenpropit, meets the criteria for a suitable radioligand for histamine H3‐receptor binding studies in rat brain.
The binding of the first selective radiolabeled histamine H3‐receptor antagonist [125I]‐iodophenpropit to rat cerebral cortex membranes was characterized.
[125I]‐iodophenpropit, radiolabeled to a high specific activity of 1900 Ci mmol‐1, saturably bound to a single class of sites with a KD of 0.57 ± 0.16 nm (n = 4) and Bmax of 268 ± 119 fmol mg‐1 protein.
Specific binding at a concentration below 1 nm represented 50 to 60% of total binding.
Binding of [125I]‐iodophenpropit to rat cerebral cortex membranes was readily displaced by histamine H3‐agonists and antagonists. In contrast, the inhibitory potencies of selective histamine H1‐ and H2‐receptor ligands were very low.
[125]‐iodophenpropit was biphasically displaced by the histamine H3‐receptor antagonists, burimamide and dimaprit, which may indicate the existence of histamine H3‐receptor subtypes. Other histamine H3‐receptor antagonists showed a monophasic displacement.
Competition binding curves of H3‐agonists were biphasic and showed a rightward shift upon the addition of the nonhydrolysable GTP analogue, guanosine 5′‐o‐(3‐thio) triphosphate (GTPγS; 100 μm) which implicates the interaction of histamine H3‐receptors with G‐proteins. The affinities of the H3‐receptor antagonists iodophenpropit, thioperamide and burimamide were not altered by GTPγS.
Histamine competition binding curves were shifted to the right by different nucleotides (100 μm) with a rank order of potency GTPγS > Gpp(NH)p, GTP.
In vitro autoradiographic studies revealed a heterogeneous distribution of [125I]‐iodophenpropit binding sites in rat brain, with highest densities observed in specific cerebral cortical areas and layers, the caudate‐putamen complex, the olfactory tubercles, the hippocampal formation, the amygdala complex, the hypothalamic area and the mammillary bodies.
It is concluded that the histamine H3‐receptor antagonist, [125I]‐iodophenpropit, meets the criteria for a suitable radioligand for histamine H3‐receptor binding studies in rat brain.
DOI: 10.1111/j.1476-5381.1994.tb16995.x
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