Characterization and localization of thromboxane A2 receptor in human and guinea‐pig nasal mucosa using radiolabelled (+)‐S‐145

• Published in: British journal of pharmacology Vol. 124; no. 4; pp. 795 - 803
• Main Authors: Arimura, A, Miwa, M, Hasegawa, H, Kishino, J, Notoya, M, Yasui, K, Komori, M, Iwata, S
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.06.1998; Nature Publishing
• Subjects: (+)‐S‐145; 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid - metabolism; Animals; Autoradiography; Binding, Competitive; Biological and medical sciences; Blood Platelets - drug effects; Blood Platelets - metabolism; Bridged Bicyclo Compounds - metabolism; Cell receptors; Cell structures and functions; Fatty Acids, Monounsaturated - metabolism; Fundamental and applied biological sciences. Psychology; Guinea Pigs; guinea‐pig nasal mucosa; human nasal mucosa; Humans; In Vitro Techniques; Iodine Radioisotopes; Miscellaneous; Molecular and cellular biology; Nasal Mucosa - drug effects; Nasal Mucosa - metabolism; Radioligand Assay; receptor autoradiography; Receptors, Thromboxane - agonists; Receptors, Thromboxane - antagonists & inhibitors; Receptors, Thromboxane - metabolism; S‐1452; Thromboxane A2; Thromboxane A2 - metabolism; TP‐receptor; Human; Agonist; Mucosa; Thromboxane A2; Rodentia; ENT; Autoradiography; Vertebrata; Biological fixation; Platelet; Mammalia; Guinea pig; Nose; Antagonist; Radiopharmaceuticals; Labelled compound; Biological receptor
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0701904

TxA2 receptor (TP‐receptor) antagonists such as S‐1452 and Bay u 3405 have been shown to be effective in alleviating nasal blockage in patients with allergic rhinitis as well as guinea‐pig allergic rhinitis models. The present study was conducted to examine the existence and localization of the TP‐receptor in human and guinea‐pig nasal mucosa by in vitro receptor binding autoradiography using radiolabelled (+)‐S‐145, which is a potent and specific TP‐receptor antagonist with an extremely slow dissociation rate. We ascertained the binding specificity of [3H]‐(+)‐S‐145 in human and guinea‐pig platelet membranes by comparing the ability of four TP‐receptor ligands of U‐46619, (+)‐S‐145, I‐(+)‐S‐145 and Bay u 3405 to displace the specific binding of [3H]‐(+)‐S‐145 and [3H]‐U‐46619. The rank order of potency (Ki) for the displacement was correlated highly with that determined from [3H]‐U‐46619 binding to the same preparations. Quantitative autoradiography using a radioluminographic imaging plate system, in which the radioactivity of [3H]‐(+)‐S‐145 is expressed as photostimulated luminescence (PSL) per area (mm2), revealed that specific binding of [3H]‐(+)‐S‐145 to human and guinea‐pig nasal mucosa was saturable. Scatchard analysis showed about three fold higher affinity and two fold greater maximal binding to the nasal mucosa of humans than that of guinea‐pigs: the KD and Bmax values in human mucosa were 2.82±0.35 nM and 6.47±0.33 PSL mm−2 and those in guinea‐pig mucosa were 8.23±1.93 nM and 3.37±0.66 PSL mm−2, respectively. Specific [3H]‐(+)‐S‐145 binding to cryostat sections of human and guinea‐pig nasal mucosa was displaced by another TP‐receptor antagonist, Bay u 3405, and a TP‐receptor agonist, U‐46619. The order of potency (Ki value: nM) was (+)‐S‐145 (2.5) > Bay u 3405 (15.4) >> U‐46619 (359.6) in human nasal mucosa and (+)‐S‐145 (22.8) > U‐46619 (49.8) & Bay u 3405 (62.1) in guinea‐pig nasal mucosa. These rank orders showed rather good correlation with those obtained for the respective platelet membranes. Autoradiographs of human nasal mucosa demonstrated that specific [125I]‐(+)‐S‐145 binding sites mainly exist on the smooth muscle layers of venous sinusoids and arterioles in the lamina propria, with few or no binding sites in the epithelium and nasal gland. We concluded that radiolabelled (+)‐S‐145 can be used as a TP‐receptor ligand for autoradiographic study, and that the TP‐receptor is exclusively located on smooth muscle layers of venous sinusoids and arterioles in the nasal mucosa. The potent vasoconstrictive activity of TxA2 may cause reduction of local blood flow followed by mucosal oedema probably through mechanisms of vascular injury such as ischaemia‐reperfusion.