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Imidazoline Receptors in Vascular Smooth Muscle and Endothelial Cells fn1
Author(s) -
REGUNATHAN SOUNDARARAJAN,
YOUNGSON CHARLOTTE,
WANG HONG,
REIS DONALD J.
Publication year - 1995
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.1749-6632.1995.tb32453.x
Subject(s) - receptor , vascular smooth muscle , chemistry , endocrinology , microbiology and biotechnology , medicine , biology , smooth muscle , biochemistry
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.