SELECTIVITY OF ENDOTOXIN-INDUCED DEFECT IN ENDOTHELIAL CALCIUM MOBILIZATION

Background. We hypothesized that endotoxin (LPS) would impair bradykin in (BK)-induced calcium (Ca2+) mobilization in aortic endothelial cell s, perhaps due to cytotoxicity or via stimulation of nitric oxide (NO) synthesis. As well, we sought to define contributions of LPS-stimulat ed Ca2+ mobilization to these effects. Methods. LPS- or BK-induced inc rements of intracellular Ca2+ were assessed by microspectrofluorimetry with fura-2 in passaged bovine aortic endothelial cells. Time- and do se-dependent effects of LPS exposure (+/- inhibitors of NO or prostagl andin synthesis) on subsequent BK-induced Ca2+ mobilization and on att ached cell counts were determined. Results. LPS (0.1 to 1.0 mg/ml) led to rapid increments of Ca2+ while Ca2+ responses were delayed followi ng LPS (1 to 10 mu g/ml) and lower doses were without effect. By contr ast, LPS more potently (1.0 pg to 1.0 mu g/ml) led to dose- and time-d ependent impairment of subsequent BK-induced Ca2+ mobilization, with p eak effect at four to six hours. persisting for at least 18 hours. Thi s delayed effect on BK-response was unaltered by inhibition of either NO synthase or cyclooxygenase. The effect of LPS on BK-responsivity de pended importantly on cell confluence, as it was not observed in subco nfluent cells. By contrast, LPS-induced cell detachment, which was obs erved only at doses greater than or equal to 1.0 mu g/ml, did not depe nd on confluence. Conclusions. Different mechanisms lead to endothelia l cytotoxicity and to impaired BK-response following LPS. Only the for mer effect, occurring at higher doses, might depend on initial LPS-ind uced Ca2+ mobilization.