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.