Binding of
cyclic AMP to the regulatory subunit of
cyclic AMP-dependent protein kinase (PKA) is an essential step in
cyclic AMP-mediated intracellular signal transduction. This binding is, however, rapidly inhibited in the acute phase of
cerebral ischemia, indicating that the signal transduction via PKA is very vulnerable to
ischemia, although this signal pathway is very important for neuronal survival in the brain. Several lines of evidence suggest that the activation of voltage-sensitive Na+ and Ca(2+) channels is an important mediator of acute ischemic brain damage. In the present study, therefore, we examined the effect of a novel Na+ and Ca(2+) channel blocker,
NS-7 (4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride), on changes in the binding activity of PKA to
cyclic AMP in permanent focal
cerebral ischemia, which was induced by occlusion of the middle cerebral artery by the intraluminal
suture method for 5 h in the rat.
NS-7 (1 mg/kg) or saline was intravenously infused 5 min after occlusion. The binding activity of PKA to
cyclic AMP and local cerebral blood flow were assessed by the in vitro [(3)H]
cyclic AMP binding and the [(14)C]
iodoantipyrine methods, respectively.
NS-7 significantly suppressed inhibition of the binding activity of PKA to
cyclic AMP in the ischemic regions such as the frontal and parietal cortices and the medial region of the caudate-putamen without affecting cerebral blood flow or arterial blood pressure.
Infarct area measured in the brain slices stained with
cresyl violet was significantly smaller in animals treated with
NS-7 than in those treated with saline. Blockade of voltage-sensitive Na+ and Ca(2+) channels by
NS-7 was expected to reduce
ischemia-induced depolarization and thus prevent a massive formation of
free radicals, which is known to inhibit the binding activity of PKA to
cyclic AMP. These data clearly indicate that
NS-7 provides very efficient neuroprotection in the acute phase of
cerebral ischemia, and sustains the normal function of PKA.