The relationship between
nitric oxide (NO) and intracellular Ca2+ in hypoxic-ischemic brain damage is not known in detail. Here we used rat striatal slices perfused under low-
oxygen and Ca2+-free conditions and cultured human
astrocytoma cells incubated under similar conditions as models to study the dynamics of intracellular NO and Ca2+ in
hypoxia-induced tissue damage. Exposure of rat striatal slices for 70 min to low
oxygen tension elicited a delayed and sustained increase in the release of 45Ca2+. This was potentiated by the NO donors
sodium nitroprusside (SNP) and
spermine-NO and inhibited by
N-omega-nitro-L-arginine methyl ester (
L-NAME) or by the NO scavenger 2-phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl-3-oxide (
PTIO). A membrane-permeant form of
heparin in combination with either
ruthenium red (RR) or
ryanodine (RY) also inhibited 45Ca2+ release. In human
astrocytoma U-373 MG cells,
hypoxia increased intracellular Ca2+ concentration ([Ca2+]i) by 67.2 +/- 13.1% compared to normoxic controls and this effect was inhibited by
L-NAME,
PTIO or
heparin plus RR. In striatal tissue,
hypoxia increased NO production and LDH release and both effects were antagonized by
L-NAME. Although
heparin plus RR or RY antagonized
hypoxia-induced increase in LDH release they failed to counteract increased NO production. These data therefore indicate that NO contributes to hypoxic damage through increased intracellular Ca2+ mobilization from endoplasmic reticulum and suggest that the NO-Ca2+ signalling might be a potential therapeutic target in
hypoxia-induced neuronal degeneration.