Protein kinase C isoforms changes induced by chemical ischemia-reperfusion in rat cerebral cortex slices

The aim of the present report was to study the role played by PKCs in during brain ischemia, comparing the effects of oxygen-glucose deprivation (1) to the changes induced by chemical ischemia in vitro. Superfused rat cerebral cortex slices were submitted to continuous electrical (5 Hz) stimulation and treated for 5min with NaN3, in the presence of 2 mM 2-deoxyglucose (“chemical ischemia”). The study was carried out in control as well as in treated slices, both immediately, and one hour after chemical ischemia (reperfusion); subcellular (cytosol and membrane) distribution of PKC isoforms was determined by Western blot analysis using specific antibodies against PKC isoforms α, β1, β2, γ, δ and ε. In control samples all the isoforms were detected; immediately after chemical ischemia, PKC β1, δ and ε isoforms total levels (cytosol + membrane) were increased to 291+21%, 277+23% and 994+33%, respectively, while γ isoform was no more detectable. After reperfusion the changes displayed by β1, γ, δ and ε were maintained; moreover, a reduction in PKC α (39.5+10%) and an increase in β2 (141+12%) total levels became significant. The activation of PKC isoforms was evaluated by the “translocation index” (membrane to total ratio). Chemical ischemia induced a significant activation in PKC α isoform, which was completely lost during reperfusion. PKC β1 and δ isoforms were significantly activated both in ischemic and in reperfused samples, in comparison to the controls; the NMDA antagonist, MK801, 1μM, was not able to antagonize these effects. During reperfusion, the increase in PKC 2 and  isoforms total levels was not accompanied by an increase in translocation index and even a reduction was displayed. Since MK801 antagonized the latter effect, the changes observed during reperfusion, indicative of neuronal damage, suggest glutamate involvement. In agreement with our previous data with oxygen-glucose deprivation (1), PKC isoforms appear to differently participate in the events triggered by in vitro ischemia and a peculiar role for 2 and  isoforms in neurotoxicity/neuroprotection may be inferred. However, the activation of β1 and δ isoforms suggest different mechanisms underlying chemical ischemia. (1) Selvatici R., Marino S., Piubello C., Rodi D., Beani L., Gandini E. and Siniscalchi A. (2003) J Neurosci Res 71, 64-71.