Effect of cell density on endothelin release from endothelial cells and phosphoramidon dependent inhibition

The modulation of endothelin (ET) release from endothelial cells was investigated as a function of cell density. The present study examined the release of ET from bovine pulmonary artery endothelial cells (BPAEC) and bovine aortic endothelial cells (BAEC) at various cell densities, as well as the effects of phosphoramidon, thiorphan and pepstatin on ET release at different densities. ET release from BPAEC and BAEC decreased as cell density increased. This cell density effect was not observed with prostacyclin release from either BPAEC or BAEC. Phosphoramidon (1 mM) inhibited ET release at every density examined for both BPAEC and BAEC. Thiorphan (1 mM) inhibited ET release from BPAEC weakly at low density and had no effect on ET release from BAEC. Pepstatin (1 mM) slightly inhibited ET release in BPAEC at the lowest density and had no effect at any other cell density for either cell type. These protease inhibitors had no effect on cell viability as determined by trypan blue exclusion and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide conversion assay. This study supports the concept that ET release is modulated by endothelial cell density. In addition, these data demonstrate that phosphoramidon, which presumably inhibits the endothelin converting enzyme, can inhibit ET release over a range of cell densities without affecting cell viability.