The function and regulation of
Na(+)/H(+) exchanger isoform 1 (NHE1) following
cerebral ischemia are not well understood. In this study, we demonstrate that extracellular signal-related
kinases (ERK1/2) play a role in stimulation of neuronal NHE1 following in vitro
ischemia. NHE1 activity was significantly increased during 10-60 min reoxygenation (REOX) after 2-h
oxygen and
glucose deprivation (OGD). OGD/REOX not only increased the V(max) for NHE1 but also shifted the K(m) toward decreased [H(+)](i). These changes in NHE1 kinetics were absent when
MAPK/ERK kinase (
MEK) was inhibited by the
MEK inhibitor
U0126. There were no changes in the levels of phosphorylated ERK1/2 (p-ERK1/2) after 2 h OGD. The p-ERK1/2 level was significantly increased during 10-60 min REOX, which was accompanied by nuclear translocation.
U0126 abolished REOX-induced elevation and translocation of p-ERK1/2. We further examined the ERK/90-kDa ribosomal
S6 kinase (
p90(RSK)) signaling pathways.
At 10 min REOX, phosphorylated NHE1 was increased with a concurrent elevation of phosphorylation of
p90(RSK), a known NHE1
kinase. Inhibition of
MEK activity with
U0126 abolished phosphorylation of both NHE1 and
p90(RSK). Moreover, neuroprotection was observed with
U0126 or genetic ablation or pharmacological inhibition of NHE1 following OGD/REOX. Taken together, these results suggest that activation of ERK1/2-
p90(RSK) pathways following in vitro
ischemia phosphorylates NHE1 and increases its activity, which subsequently contributes to neuronal damage.