When ischemic brain is reperfused, there is in vulnerable neurons immediate
inhibition of protein synthesis associated with a large increase in phosph
orylation of the alpha-subunit of eukaryotic initiation factor 2 [eIF2 alph
a, phosphorylated form eIF2 alpha(P)]. We examined eIF2 alpha kinase and eI
P2 alpha(P) phosphatase activity in brain homogenate postmitochondrial supe
rnatants obtained from rats after 3 to 30 min of global brain ischemia (car
diac arrest), after 5 min of ischemia and 5 min of reperfusion (5R), and af
ter 10 min of ischemia and 90 min reperfusion (90R), Because it has been su
ggested that PKR might be specifically responsible for producing eIF2 alpha
(P) during reperfusion, we also examined in brain homogenates from wild-typ
e and PKR0/0 C57BL/6J x 129/SV mice the effect of 5 min of ischemia and 5 m
in of reperfusion on eIF2 alpha(P). Cytosolic brain elF2 alpha(P) in the 5R
and 90R rats was 18- and 23-fold that of nonischemic controls without any
change in the rate of elF2 alpha(P) dephosphorylation. There was no change
in eIF2 alpha kinase activity between 3 and 30 min of ischemia but an 85% d
ecrease in the 5R group; the 90R group was similar to controls. In wild-typ
e and PKR0/0 mice total eIF2 alpha was identical, and there was an identica
l le-fold increase in eIF2 alpha(P) at 5 min of reperfusion. Our observatio
ns contradict hypotheses that PKR activation, loss of eIF2 alpha(P) phospha
tase activity, or any general increase in eIF2 alpha kinase activity are re
sponsible for reperfusion-induced phosphorylation of eIF2 alpha, and we sug
gest that the mechanism may involve regulation of the availability of eIF2
alpha to a kinase. (C) 1999 Academic Press.