Biochemical cascades initiated by oxidative stress and excitotoxic intracellular
calcium rises are thought to converge on
mitochondrial dysfunction. We investigated the contribution of
mitochondrial dysfunction to
free radical (FR) overproduction in rat CA1 pyramidal neurons of organotypic slices subjected to a hypoxic-
hypoglycemic insult.
Ischemia-induced FR generation was decreased by the mitochondrial complex I blocker,
rotenone, indicating that mitochondria are the principal source of ischemic FR production. Measurements of mitochondrial
calcium with the mitochondrial
calcium probe dihydroRhod-2, revealed that FR production during and after the anoxic episode correlates with the accumulation of mitochondrial
calcium. However, the mitochondrial
calcium uptake inhibitor
Ru360 did not prevent FR generation during
ischemia and attenuated it to some degree during reoxygenation. On the other hand, the mitochondrial permeability transition blocker cyclosporinA (CsA) completely arrested both ischemic FR generation and mitochondrial
calcium overload, and prevented deterioration of neuronal intrinsic membrane properties. CsA had no effect on the accumulation of intracellular
calcium during
ischemia-reperfusion.
Nicotinamide, a blocker of NAD+ hydrolysis, reproduced the CsA effects on FR generation, mitochondrial
calcium accumulation and cytoplasmic
calcium increases. These observations suggest that a major determinant of ischemic FR generation in pyramidal neurons is the uncoupling of the mitochondrial respiratory chain, which may be associated with the mitochondrial permeability transition.