Human brain imidazoline receptors: further characterization with [3H]clonidine

Item Type:	Article
Title:	Human brain imidazoline receptors: further characterization with [3H]clonidine
Creators Name:	Bricca, G. and Greney, H. and Zhang, J. and Dontenwill, M. and Stutzmann, J. and Belcourt, A. and Bousquet, P.
Abstract:	The aim of the present study was to further characterize [3H]clonidine binding in the ventrolateral medulla of the human brainstem, the region involved in the vasodepressor effect of imidazoline drugs of the clonidine type. Under basal conditions, [3H]clonidine can bind both to the imidazoline receptors and to the alpha-adrenoceptors. The latter represent only a small part of the total [3H]clonidine binding with a Bmax of 61 +/- 13 fmol/mg proteins and a KD of 4.9 +/- 2.2 nM. Most of the binding was associated with imidazoline receptors with a KD of 67 +/- 13 nM and a Bmax of 677 +/- 136 fmol/mg protein. alpha-Adrenoceptor binding of [3H]clonidine could be completely prevented when membranes were either treated during preparation with the aIkylating agent phenoxybenzamine or incubated in the presence of 30 microM (-)-noradrenaline or in the presence of the non-hydrolysable analogue of GTP, guanylyl imidodiphosphate (Gpp(NH)p). When the alpha-adrenoceptors binding was prevented, we demonstrated the insensitivity of [3H]clonidine binding to Gpp(NH)p and showed that the competition between clonidine and idazoxan for imidazoline receptors was insensitive to Gpp(NH)p suggesting that imidazoline receptors are not G protein coupled receptors. The specificity of [3H]cloniding binding to imidazoline receptors in the human ventrolateral medulla indicates that these receptors are different from imidazole receptors as defined with p-aminoclonidine in the bovine brainstem.
Keywords:	Competitive Binding, Brain Stem, Clonidine, Guanylyl Imidodiphosphate, Imidazoline Receptors, Naphazoline, Adrenergic, Alpha Receptors, Drug Receptors
Source:	European Journal of Pharmacology - Molecular Pharmacology Section
ISSN:	0014-2999
Volume:	266
Number:	1
Page Range:	25-33
Date:	1 January 1994
PubMed:	View item in PubMed

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