Protein kinase C activity, translocation, and selective isoform subcellular redistribution in the rat cerebral cortex after in vitro ischemia

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Abstract
Protein kinase C (PKC) involvement in ischemia‐induced neuronal damage has been investigated in superfused rat cerebral cortex slices submitted to 15 min of oxygen‐glucose deprivation (OGD) and in primary cultures of rat cortical neurons exposed to 100 μM glutamate (GLU) for 10 min. OGD significantly increased the total PKC activity in the slices, mostly translocated in the particulate fraction. After 1 hr of reperfusion, the total PKC activity was reduced and the translocated fraction dropped by 84% with respect to the control. Western blot analysis of OGD samples showed an increase in total β2 and ϵ PKC isoform levels. After reperfusion, the total levels of α, β1, β2 and γ isoforms were significantly reduced, whereas the ϵ isoform remained at an increased level. Endogenous GLU release from OGD slices increased to about 15 times the basal values after 15 min of oxygen‐glucose deprivation, and to 25 and 35 times the basal level in the presence of the PKC inhibitors staurosporine (0.1 μM) and bisindolylmaleimide (1 μM), respectively. Western blot analysis of GLU‐treated cortical neurons showed a significant decrease only in the total level of β2 isoforms. Cell survival was reduced to 31% in GLU‐treated neuronal cultures; PKC inhibitors were not able to modify this effect. These findings demonstrate that the cell response to OGD and GLU involves PKC in a complex way. The net role played by PKC during OGD may be to reduce GLU release and, consequently, neurotoxicity. The isoforms β2 and ϵ are affected the most and may play a significant role in the mechanisms underlying neurotoxicity/neuroprotection.

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