The effect of
anoxia on Na+/H+ exchange activity was examined in acutely isolated adult rat hippocampal CA1 neurons loaded with the H+-sensitive fluorophore,
BCECF. Five-minute
anoxia imposed under nominally HCO3-/CO2-free conditions induced a fall in pHi, the magnitude of which was smaller following prolonged exposure to medium in which N-methyl-D-glucamine (NMDG+) was employed as an extracellular Na+ (Na(+)(o)) substitute. Also consistent with the possibility that Na+/H+ exchange becomes inhibited soon after the induction of
anoxia, rates of Na(+)(o)-dependent pHi recovery from internal
acid loads imposed during
anoxia were slowed, compared to rates of Na(+)(o)-dependent pHi recovery observed prior to
anoxia. At the time at which rates of pHi recovery were reduced during anoxia, cellular
adenosine triphosphate (
ATP) levels had fallen to 35% of preanoxic levels, suggesting that
ATP depletion might contribute to the observed inhibition of Na+/H+ exchange. In support, incubation of neurons with
2-deoxyglucose and
antimycin A under normoxic conditions induced a fall in cellular
ATP levels that was also associated with reduced Na(+)(o)-dependent rates of pHi recovery from imposed
acid loads; conversely, pre-treatment with 10 mm
creatine attenuated the effects of
anoxia to reduce both
ATP levels and Na(+)(o)-dependent rates of pHi recovery from internal
acid loads. Taken together, the results are consistent with the possibility that functional Na+/H+ exchange activity in adult rat CA1 neurons declines soon after the onset of
anoxia, possibly as a result of
anoxia-induced falls in intracellular
ATP.