title: Imidazoline receptors in vascular smooth muscle and endothelial cells.
abstract: We sought to determine if smooth muscle and endothelial cells of blood vessels express imidazoline receptors. Membranes of cultured smooth muscle cells specifically bind with high affinity to alpha 2-adrenergic ligands, [3H]p-aminoclonidine, [3H]rauwolscine, and [3H]idazoxan. All of [3H]rauwolscine and [3H]p-aminoclonidine but less than 10% of [3H]idazoxan binding was displaced by 10 microM epinephrine, indicating a nonadrenergic binding site for [3H]idazoxan. [3H]Idazoxan binding was inhibited with a rank order of potency: cirazoline > idazoxan > naphazoline >> guanabenz > amiloride > clonidine = phentolamine. Agmatine, an endogenous ligand for I-receptors, inhibited binding with a Ki of 240 +/- 25 nM. The binding of [3H]idazoxan to membranes of pulmonary artery endothelial cells was to both alpha 2-adrenergic and imidazoline receptors. Cultured smooth muscle cells, as well as rat carotid arterioles, were specifically immunostained by antibodies to an I-receptor-associated protein. We conclude that vascular smooth muscle and endothelial cells express not only alpha 2-adrenergic receptors but also I-receptors of the I2 subclass with high affinity for agmatine. Since serum contains an endogenous ligand for I-receptors, possibly agmatine, the results suggest the presence of a novel receptor mechanism on vascular smooth muscle which may regulate vascular tone.
authors.affiliation: Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021, USA.
authors.forename: S
authors.initials: S
authors.lastname: Regunathan
authors.forename: C
authors.initials: C
authors.lastname: Youngson
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: D J
authors.initials: DJ
authors.lastname: Reis
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism*; D054755:Imidazoline Receptors; D007106:Immune Sera; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D011955:Receptors, Drug / Q000276:immunology / Q000378:metabolism*
chemical_list: D007093:Imidazoles; D054755:Imidazoline Receptors; D007106:Immune Sera; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug