Pt. Murray et al., ENDOTOXIN IMPAIRS AGONIST-INDUCED CALCIUM MOBILIZATION IN RAT MESANGIAL CELLS, American journal of respiratory and critical care medicine, 156(6), 1997, pp. 1846-1854
We hypothesized that endotoxin would impair agonist-induced calcium (C
a2+) mobilization in rat mesangial cells, owing to the induction of ni
tric oxide synthase (NOS) and augmented nitric oxide (NO) synthesis. W
e measured basal and bradykinin-induced peak free cytosolic Ca2+ conce
ntrations through microspectrofluorimetry with fura-2 in confluent mes
angial cells, and assayed conditioned medium for nitrite accumulation.
Prior to measurement, cells were incubated overnight in serum-supplem
ented medium, with or without endotoxin, L-arginine, indomethacin, mec
lofenamate, or N-(sic)-nitro-Larginine methyl ester (L-NAME). Endotoxi
n (1 mg/ml) decreased bradykinin-induced peak Ca2+ responses by 35 to
60% (p < 0.0001) and increased nitrite accumulation > B-fold (p < 0.01
). Arginine supplementation further (> 9-fold, p < 0.0001) increased n
itrite accumulation without changing the effect on Ca2+. Inhibition of
NOS abolished increments in nitrite concentration but had no effect o
n impaired Ca2+ responses. Cyclooxygenase (COX) inhibitors, present du
ring incubation with endotoxin, but not afterward, normalized bradykin
in-stimulated calcium responses. Thrombin-stimulated Ca2+ responses we
re similarly affected. We conclude that neither NO nor prostaglandins
act directly to impair agonist-induced Ca2+ mobilization following end
otoxin exposure; however, this effect may be an indirect effect of COX
products, including reactive oxygen intermediates.