Effects of NP-1815-PX, a P2X4 Receptor Antagonist, on Contractions in Guinea Pig Tracheal and Bronchial Smooth Muscles.

Administration of a P2X4 receptor antagonist to asthma model mice improved asthma symptoms, suggesting that P2X4 receptor antagonists may be new therapeutics for asthma. However, the effects of these antagonists on tracheal/bronchial smooth muscle (TSM and BSM) have not been investigated. This study examined the effects of NP-1815-PX, a selective P2X4 receptor antagonist, on guinea pig TSM and BSM contractions. In epithelium-intact TSM, NP-1815-PX (10 M) strongly suppressed ATP-induced contractions. ATP-induced contractions were strongly suppressed by indomethacin (3 × 10 M) and ONO-8130 (a prostanoid EP receptor antagonist, 10 M). ATP-induced contractions were partially suppressed by SQ 29,548 (a prostanoid TP receptor antagonist, 3 × 10 M), although the difference was not significant. In contrast, ATP-induced contractions were not affected by AL 8810 (a prostanoid FP receptor antagonist, 10 M) or L-798,106 (a prostanoid EP receptor antagonist, 10 M). NP-1815-PX (10-10 M) strongly suppressed U46619 (a TP receptor agonist)- and prostaglandin F (PGF)-induced epithelium-denuded TSM and BSM contractions, which were largely inhibited by SQ 29,548. Additionally, NP-1815-PX (10-10 M) strongly suppressed the U46619-induced increase in intracellular Ca concentrations in human TP receptor-expressing cells. However, NP-1815-PX (10 M) did not substantially inhibit the TSM/BSM contractions induced by carbachol, histamine, neurokinin A, or 50 mM KCl. These findings indicate that NP-1815-PX inhibits guinea pig TSM and BSM contractions mediated through the TP receptor, in addition to the P2X4 receptor, whose stimulation mainly induces EP receptor-related mechanisms. Thus, these findings support the usefulness of NP-1815-PX as a therapeutic drug for asthma.