Role of EETs in regulation of endothelial permeability in rat lung

Abstract

This study tested the hypothesis that epoxyeicosatrienoic acids (EETs) derived from arachidonic acid via P-450 epoxygenases are soluble factors linking depletion of endoplasmic reticulum Ca²⁺ stores and store-dependent regulation of endothelial cell (EC) permeability in rat lung. EC permeability was measured via the capillary filtration coefficient ( K_f,c) in isolated, perfused rat lungs. 14,15-EET and 5,6-EET increased EC permeability, a response that was significantly different from that of 8,9-EET, 11,12-EET, and vehicle control. The permeability response to 14,15-EET was not significantly attenuated by the nonspecific Ca²⁺ channel blocker Gd³⁺ ( P = 0.068). In lungs perfused with low [Ca²⁺], 14,15-EET tended to increase EC permeability, although a significant increase in K_f,c was observed only following Ca²⁺ add-back. As positive control, we showed that the 3.7-fold increase in K_f,c evoked by thapsigargin (TG), a known activator of store depletion-induced Ca²⁺ entry, was blocked by both Gd³⁺ and low [Ca²⁺] buffer. Nonetheless, the permeability response to TG could not be blocked by the phospholipase A₂ inhibitors mepacrine or methyl arachidonyl fluorophosphonate or the P-450 epoxygenase inhibitors 17-octadecynoic acid or propargyloxyphenyl hexanoic acid. Similarly, combined pretreatment with ibuprofen and dicyclohexylurea to block EET metabolism had no effect on the permeability response to TG. We conclude that EETs have a heterogeneous impact on EC permeability. Despite a requirement for Ca²⁺ entry with both TG and 14,15-EET, our data suggest that distinct signaling pathways or heterogeneity in EC responsiveness is responsible for the observed EC injury evoked by EETs and store depletion in the isolated rat lung.