# Involvement of Nitric Oxide in TRPV4-Induced Relaxations of Mouse and Human Pulmonary Arteries

## TL;DR

This study shows that TRPV4 channels help relax lung blood vessels by boosting nitric oxide production, which could lead to new treatments for lung diseases like pulmonary hypertension.

## Contribution

The study reveals TRPV4 channels regulate pulmonary vascular tone via nitric oxide, independent of KCa3.1 channels.

## Key findings

- TRPV4 activation increases nitric oxide and relaxation in mouse and human pulmonary arteries.
- TRPV4-induced relaxation remains functional even without KCa3.1 channels.
- Endothelium-dependent relaxation via TRPV4 is mediated by nitric oxide in human arteries.

## Abstract

Lung diseases, such as pulmonary hypertension and acute lung injury, are driven by abnormal narrowing of blood vessels and damage to the vessel lining, which can lead to heart failure and impaired oxygen delivery. In this study, we investigated how a specific calcium pathway in blood vessel cells regulates vasorelaxation by releasing nitric oxide and activating potassium channels. Using mouse models and human lung blood vessels, we found that activation of this calcium pathway strongly promotes vessel relaxation by increasing nitric oxide production and electrical signaling that relaxes the smooth muscle cells. This mechanism remained functional even when certain potassium channels were absent, which indicates the presence of compensatory protective pathways. Our results show that this calcium signaling system plays a central role in controlling lung blood vessel tone under both healthy and disease conditions. These findings are valuable because they identify potential therapeutic targets that could be used to relax lung blood vessels in pulmonary hypertension.

The transient receptor potential vanilloid 4 channel (TRPV4) is thought to play a pivotal role in pulmonary arterial circulation. The present study hypothesizes that TRPV4 activation increases nitric oxide (NO) release and activates calcium-activated potassium of intermediate conductance (KCa3.1) in pulmonary arteries. Pulmonary arteries were isolated from wild-type mice (wt) and mice deficient in KCa3.1 channels (Kcnn4−/−) and mounted for simultaneous NO concentration and relaxation measurements. Human small pulmonary arteries were isolated and mounted in microvascular myographs for isometric tension recordings. Acetylcholine-induced increases in NO and relaxation of pulmonary arteries were slightly decreased in pulmonary arteries from Kcnn4−/− versus wt mice. An activator of TRPV4 channels, GSK1016790A, increased NO and relaxation to the same degree in pulmonary arteries from wt and Kcnn4−/− mice. A blocker of TRPV4 channels, HC06704, inhibited increases in NO concentration with no effect on acetylcholine (ACh) relaxation in pulmonary arteries from wt mice, but blocked increases in NO concentration and relaxation in pulmonary arteries from Kcnn4−/− mice and responses to GSK1016790A in pulmonary arteries from wt and Kcnn4−/− mice. Concentration-dependent relaxations induced by an inhibitor of sarcoplasmic Ca-ATPase, cyclopiazonic acid, were blocked in the presence of an inhibitor of NO synthase and a blocker of KCa3.1 channels, TRAM-34, in pulmonary arteries from wt mice, but were unaltered in the presence of TRAM-34 in arteries from Kcnn4−/− mice, or the presence of a blocker of TRPV4 channels. In small human pulmonary arteries, ACh and sodium nitroprusside (SNP) induced concentration-dependent relaxations, blocked by endothelial cell removal, in the presence of an inhibitor of NO synthase and the KCa3.1 channel blocker TRAM-34. GSK1016790A induced relaxation of human pulmonary arteries with endothelium, but failed to relax arteries without endothelium. The findings suggest that TRPV4 channels are involved in endothelium-dependent relaxation and likely regulate pulmonary vascular tone by modulating NO release.