PROTEIN-KINASE-C EXPRESSION AND ACTIVITY AFTER GLOBAL INCOMPLETE CEREBRAL-ISCHEMIA IN DOGS

Background and Purpose-Studies suggest that protein kinase C (PKC) act ivation during ischemia plays an important role in glutamate neurotoxi city and that PKC inhibition may be neuroprotective. We tested the hyp othesis that elevations in the biochemical activity and protein expres sion of Ca2+-dependent PKC isoforms occur in hippocampus and cerebellu m during the period of delayed neurodegeneration after mild brain isch emia. Methods-We used a dog model of 20 minutes of global incomplete i schemia followed by either 6 hours, 1 day, or 7 days of recovery. Chan ges in PKC expression (Western blotting and immunocytochemistry) and b iochemical activity were compared with neuropathology (percent ischemi cally damaged neurons) by means of hematoxylin and eosin staining. Res ults-The percentage of ischemically damaged neurons increased from 134% to 52+/-10% in CA1 and 24+/-11% to 69+/-6% in cerebellar Purkinje c ells from 1 to 7 days, respectively. The occurrence of neuronal injury was accompanied by sustained increases in PKC activity (240% and 211% of control in hippocampus and cerebellum, respectively) and increased protein phosphorylation as detected by proteins containing phosphoser ine residues, By Western blotting, the membrane-enriched fraction show ed postischemic changes in protein expression with increases of 146+/- 64% of control in hippocampal PKC alpha and increases of 138+/-38% of control in cerebellar PKC alpha, but no changes in PKC beta and PKC ga mma were observed. By immunocytochemistry, the neuropil of CA1 and CA4 in hippocampus and the radial glia in the molecular layer of cerebell um showed increased PKC alpha expression after ischemia. Conclusions-T his study shows that during the period of progressive ischemic neurode generation there are regionally specific increases in PKC activity, is oform-specific increases in membrane-associated PKC, and elevated prot ein phosphorylation at serine sites.