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^-5 M) strongly suppressed ATP-induced contractions. ATP-induced contractions were strongly suppressed by indomethacin (3 × 10^-6 M) and ONO-8130 (a prostanoid EP₁ receptor antagonist, 10^-7 M). ATP-induced contractions were partially suppressed by SQ 29,548 (a prostanoid TP receptor antagonist, 3 × 10^-7 M), although the difference was not significant. In contrast, ATP-induced contractions were not affected by AL 8810 (a prostanoid FP receptor antagonist, 10^-5 M) or L-798,106 (a prostanoid EP₃ receptor antagonist, 10^-8 M). NP-1815-PX (10^-5-10^-4 M) strongly suppressed U46619 (a TP receptor agonist)- and prostaglandin F_2α (PGF_2α)-induced epithelium-denuded TSM and BSM contractions, which were largely inhibited by SQ 29,548. Additionally, NP-1815-PX (10^-5-10^-4 M) strongly suppressed the U46619-induced increase in intracellular CA²⁺ concentrations in human TP receptor-expressing cells. However, NP-1815-PX (10^-4 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 EP₁ receptor-related mechanisms. Thus, these findings support the usefulness of NP-1815-PX as a therapeutic drug for asthma.

ATP; NP-1815-PX; P2X4 receptor antagonist; prostanoid EP1 receptor; prostanoid TP receptor; tracheal/bronchial smooth muscle.