Effects of ω-hydroxylase product on distal human pulmonary arteries

The aim of the present study was to provide a mechanistic insight into how 20-hydroxyeicosatetraenoic acid (20-HETE) relaxes distal human pulmonary arteries (HPAs). This compound is produced by omega-hydroxylase from free arachidonic acid. Tension measurements, performed on either fresh or 1 day-cultured pulmonary arteries, revealed that the contractile responses to 1 mu M 5-hydroxytryptamine were largely relaxed by 20-HETE in a concentration- dependent manner (0.01 - 10 mu M). Iberiotoxin pretreatments ( 10 nM) partially decreased 20-HETE-induced relaxations. However, 10 mu M indomethacin and 3 mu M SC-560 pretreatments significantly reduced the relaxations to 20-HETE in these tissues. The relaxing responses induced by the eicosanoid were likely related to a reduced Ca2+ sensitivity of the myofilaments since free Ca2+ concentration ([Ca2+])- response curves performed on beta-escin-permeabilized cultured explants were shifted toward higher [Ca2+]. 20-HETE also abolished the tonic responses induced by phorbol-ester-dibutyrate ( a PKC-sensitizing agent). Western blot analyses, using two specific primary antibodies against the PKC-potentiated inhibitory protein CPI-17 and its PKC-dependent phosphorylated isoform pCPI-17, confirmed that 20-HETE interferes with this intracellular process. We also investigated the effect of 20-HETE on the activation of Rho-kinase pathway-induced Ca2+ sensitivity. The data demonstrated that 20- HETE decreased U-46619-induced Ca2+ sensitivity on arteries. Hence, this observation was correlated with an increased staining of p116(Rip), a RhoA-binding protein. Together, these results strongly suggest that the 20- hydroxyarachidonic acid derivative is a potent modulator of tone in HPAs in vitro.