Characterization and localization of thromboxane A 2 receptor in human and guinea‐pig nasal mucosa using radiolabelled (+)‐S‐145
TxA 2 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‐...
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Veröffentlicht in: | British journal of pharmacology 2009-02, Vol.124 (4), p.795-803 |
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Sprache: | eng |
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Zusammenfassung: | TxA
2
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 [
3
H]‐(+)‐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 [
3
H]‐(+)‐S‐145 and [
3
H]‐U‐46619. The rank order of potency (
K
i
) for the displacement was correlated highly with that determined from [
3
H]‐U‐46619 binding to the same preparations.
Quantitative autoradiography using a radioluminographic imaging plate system, in which the radioactivity of [
3
H]‐(+)‐S‐145 is expressed as photostimulated luminescence (PSL) per area (mm
2
), revealed that specific binding of [
3
H]‐(+)‐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
K
D
and B
max
values in human mucosa were 2.82±0.35 n
M
and 6.47±0.33 PSL mm
−2
and those in guinea‐pig mucosa were 8.23±1.93 n
M
and 3.37±0.66 PSL mm
−2
, respectively.
Specific [
3
H]‐(+)‐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 (
K
i
value: n
M
) 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 [
125
I]‐(+)‐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 |
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ISSN: | 0007-1188 1476-5381 |
DOI: | 10.1038/sj.bjp.0701904 |