Concerted actions of TXA2 and mechanical stretch stimulate NOS3 (eNOS) in rat pulmonary arterial myocytes putatively via ROS generation and mechanosensitive channel activation (LB673)

Abstract

Nitric oxide (NO), a potent vasodilator, is produced by type 3 NO synthase (NOS3, eNOS) in endothelium. In endothelium‐denuded pulmonary arteries (PAs) from rat, however, we found that unspecific NOS inhibitor (L‐NAME) induces a weak contraction in the presence of 2 ‐ 5 nM U46619 (thromboxane A2 agonist). With additional increase in wall tension equivalent to pressure elevation to 30 mmHg (pre‐stretch), L‐NAME induced robust contraction of PAs (L‐NAME contraction; 110 % of 80 mM KCl contraction). In endothelium‐denuded systemic arteries (e.g. renal and mesenteric arteries), no such L‐NAME induced contraction was observed. Interestingly, contraction of PAs by 20 mM KCl and 2 nM U46619 was also robustly augmented by L‐NAME, suggesting that the pre‐stretch effect was mimicked by partial depolarization. Pretreatment with 30 µM DIDS, known as an inhibitor of stretch‐activated cation channels (SACs) in arterial myocytes, the L‐NAME contraction was abolished in the PAs with pre‐stretch. The L‐NAME contraction was also diminished by ROS scavengers (Tiron and PEG‐Catalase). Consistently, exogenous hydrogen peroxide (H2O2, 1 µM) effectively augmented the contraction by L‐NAME without pre‐stretch whereas 1 µM H2O2 alone had no effect. Neither NOS1 inhibitor (SMTC) nor NOS2 inhibitor (1400W) mimicked the L‐NAME contraction. Muscular expression of NOS3 was confirmed by RT‐PCR and immunohistochemistry. Taken together, we suggest that PA myocytes express NOS3 that is concertedly activated by TXA2 and mechanical stretch. ROS generation and facilitated SACs by wall stretch might mediate the NOS3 recruitment in PA myocytes, and the resultant decrease in the contractility might contribute to the relatively low peripheral resistance of pulmonary circulation with fluctuating PA pressure.