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Thromboxane A2 receptors in equine monocytes: identification of a new subclass of TXA2 receptors
Author(s) -
Simmons T. Robin,
Cook James A.,
Moore James N.,
Halushka Perry V.
Publication year - 1993
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1002/jlb.53.2.173
Subject(s) - receptor , thromboxane a2 , medicine , endocrinology , agonist , biology , stimulation , monocyte , platelet , thromboxane
Thromboxane (TX) A2 has been implicated as an important pathophysiologic mediator of a variety of cardiovascular diseases. Monocytes synthesize TXA2 and it modulates their function. This study sought to characterize monocyte TXA2 receptors. Radioligand binding studies were performed on membranes prepared from equine peripheral blood monocytes using [* 25 I]BOP, a TXA2 receptor agonist. [ 125 I]BOP bound to a single class of binding sites (Kd ‐ 1.0 ± 0.3 nM and B max = 389 ± 191 fmol/mg protein; n = 5). Several TXA2 receptor agonists and antagonists competed for binding with [ 125 I]BOP. I‐ BOP produced a concentration‐dependent inhibition of endotoxin‐induced tumor necrosis factor (TNF) activity (IC50 = 9.6 ± 2.5 nM; n = 5). In contrast to its effects in platelets and vascular smooth muscle, I‐BOP significantly increased cAMP formation in monocytes (EC50 = 22 ± 3.6 nM; n = 4). The TXA2 receptor antagonists SQ29548 (5.6 nM) and L657925 (0.13 μ M) significantly blocked I‐BOP‐ stimulated cAMP formation but did not block 250 nM prostaglandin E2‐stimulated cAMP formation. These data support the presence of a TXA2 receptor in equine peripheral blood monocytes. Activation of this receptor results in suppression of endotoxin‐induced TNF formation and stimulation of cAMP production. Increased cAMP production after receptor activation suggests that this receptor may represent a unique subclass of TXA2 receptors.