To better understand the mechanism(s) underlying nitric oxide (. NO)-mediat
ed toxicity, in the presence and absence of concomitant oxidant exposure, p
ostmitotic terminally differentiated NT2N cells, which are incapable of pro
ducing . NO, were exposed to PAPA-NONOate (PAPA/NO) and 3-morpholinosydnoni
mine (SIN-1). Exposure to SIN-1, which generated peroxynitrite in the range
of 25-750 nM/min, produced a concentration- and time-dependent delayed cel
l death. In contrast, a critical threshold concentration (>440 nM/min) was
required for . NO to produce significant cell injury. Examination of cells
by electron microscopy shows a largely necrotic injury after peroxynitrite
exposure but mainly apoptotic-like morphology after . NO exposure. Cellular
levels of reduced thiols correlated with cell death, and pretreatment with
N-acetylcysteine (NAC) fully protected from cell death in either PAPA/NO o
r SIN-1 exposure. NAC given within the first 3 h posttreatment further dela
yed cell death and increased the intracellular thiol level in SIN-1 but not
. NO-exposed cells. Cell injury from . NO was independent of cGMP, caspase
s, and superoxide or peroxynitrite formation. Overall, exposure of non-. NO
-producing cells to . NO or peroxynitrite results in delayed cell death, wh
ich, although occurring by different mechanisms, appears to be mediated by
the loss of intracellular redox balance.