Premium
Identification of Human I 1 Receptors and Their Relationship to α 2 ‐Adrenoceptors
Author(s) -
DONTENWILL M.,
VONTHRON C.,
GRENEY H.,
MAGNIER C.,
HEEMSKERK F.,
BOUSQUET P.
Publication year - 1999
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1999.tb09352.x
Subject(s) - idazoxan , imidazoline receptor , chemistry , receptor , clonidine , allosteric regulation , guanabenz , adrenergic receptor , membrane , antibody , glycosylation , biochemistry , endocrinology , biology , agonist , prazosin , antagonist , immunology
I 1 imidazoline receptors (I 1 R) were defined as receptors insensitive to catecholamines and highly sensitive to [ 3 H]clonidine and analogs. By contrast, the I 2 R subtype is more sensitive to [ 3 H]idazoxan. [ 3 H]clonidine and [ 3 H]idazoxan imidazoline specific binding sites (IBS) have been detected in crude human membranes. Pharmacologic characterization by binding assays clearly differentiates IBS from α 2 ‐adrenoceptors, whereas differences between [ 3 H]clonidine and [ 3 H]idazoxan IBS are less clear in crude preparations. In fact, only moderate affinity for [ 3 H]clonidine was detectable in such preparations. However, purification procedures allowed detection of high affinity [ 3 H]clonidine IBS in the human brain, corresponding to the I 1 R. Difficulties in the characterization of the I 1 R in crude membranes are due to multiple factors including heterogeneity of IBS, their low B max value, the existence of allosteric modulation, and possibly the presence of natural binding inhibitors. Immunologic studies with specific anti‐idiotypic antibodies revealed a 43‐kD protein as the best candidate for I 1 R as binding activity coincides with immunodetection. No cross‐reaction was found with anti‐monoamine oxidase (MAO) A/B antibodies and the 43‐kD protein, ruling out the possibility of this protein being an MAO‐associated I 2 R. Neither anti‐α 2A ‐ nor anti‐α 2B ‐specific antibodies were able to immunodetect the 43‐kD protein in crude membrane preparations or in purified fractions. These results and further biochemical characterization (pHi, N ‐glycosylation) of the 43‐kD protein definitely assessed that human brain I 1 R and α 2 ‐adrenoceptors clearly differ physically. However, coexpression of I 1 R and α 2 ‐adrenoceptors in synaptic plasma membranes of the bovine brainstem reinforce the possibility of a functional relationship between the two types of receptor.