Interest is growing in the role of
adenosine triphosphate (
ATP) on P2 receptors during hypoxic/ischemic events in the brain. However, there is no direct evidence of an increase in extracellular
ATP levels during
cerebral ischemia in vivo. The aim of the present study was to evaluate
ATP outflow from the rat striatum by the microdialysis technique associated with focal
cerebral ischemia in vivo by intraluminal occlusion of the right middle cerebral artery (MCA). Between 1 and 4h after
ischemia, rats showed a clear turning behavior contralateral to the ischemic side. Twenty-four hour after MCA occlusion, ischemic rats had definite neurological deficit and striatal and cortical damage. The
ATP concentration (mean+/-S.E.M.) in the striatum of normoxic rats (n = 8) was 3.10+/-0.34 nM. During 220 min after MCA occlusion, the extracellular
ATP levels significantly increased two-fold, being 5.90+/-0.61 nM (p < 0.01 versus normoxic level).
ATP outflow showed a tendency to increase over time during the 220 min of
ischemia. Since extracellular
ATP is rapidly metabolized to
adenosine, we also assessed
ATP outflow in the presence of the
ecto-5'-nucleotidase inhibitor, alpha,beta-methylene-
adenosine diphosphate (
AOPCP, 1 mM) directly perfused into the striatum. The
ATP concentration in normoxic rats (n = 8) was increased three-fold in the presence of the
ecto-5'-nucleotidase inhibitor (9.57+/-0.26 nM). During 220 min of
ischemia, extracellular
ATP levels significantly increased 1.3-fold in
AOPCP-treated rats (12.62+/-0.65 nM, p < 0.01 versus normoxic level). The present study confirms that
ATP is continuously released in the brain and demonstrates for the first time that
ATP outflow increases during
ischemia in vivo. These results confirm that
ATP may be an important mediator in
brain ischemia.