TRPV4 channel activation leads to endothelium-dependent relaxation mediated by nitric oxide and endothelium-derived hyperpolarizing factor in rat pulmonary artery

The purpose of the present study was to characterize TRPV4 channels in the rat pulmonary artery and examine their role in endothelium-dependent relaxation. Tension, Real-Time polymerase chain reaction (Real-Time PCR) and Western blot experiments were conducted on left and right branches of the main pulmonary artery from male Wistar rats. TRPV4 channel agonist GSK1016790A (GSK) caused concentration-related robust relaxation (Emax 88.6±5.5%; pD2 8.7±0.2) of the endothelium-intact pulmonary artery. Endothelium-denudation nearly abolished the relaxation (Emax 5.6±1.3%) to GSK. TRPV4 channel selective antagonist HC067047 significantly attenuated GSK-induced relaxation (Emax 56.2±6.6% vs. control Emax 87.9±3.3%) in endothelium-intact vessels, but had no effect on either ACh-induced endothelium-dependent or SNP-induced endothelium-independent relaxations. GSK-induced relaxations were markedly inhibited either in the presence of NO synthase inhibitor L-NAME (Emax 8.5±2.7%) or sGC inhibitor ODQ (Emax 28.1±5.9%). A significant portion (Emax 30.2±4.4%) of endothelium-dependent relaxation still persisted in the combined presence of L-NAME and cyclooxygenase inhibitor indomethacin. This EDHF-mediated relaxation was sensitive to inhibition by 60mM K+ depolarizing solution or K+ channel blockers apamin (SKCa; KCa2.3) and TRAM-34 (IKCa; KCa3.1). GSK (10−10−10−7M) caused either modest decrease or increase in the basal tone of endothelium-intact or denuded rings, respectively. We found a greater abundance (>1.5 fold) of TRPV4 mRNA and protein expressions in endothelium-intact vs. denuded vessels, suggesting the presence of this channel in pulmonary endothelial and smooth muscle cells as well. The present study demonstrated that NO and EDHF significantly contributed to TRPV4 channel-mediated endothelium-dependent relaxation of the rat pulmonary artery.