Differential subcellular redistribution of protein kinase C isozymes in the rat hippocampus induced by kainic acid

Protein kinase C (PKC) consists of a family of Ca2+/phospholipid-dependent isozymes that has been implicated in the delayed neurotoxic effects of glut amate in vitro. In the present study, we assessed the effect of the glutama te analogue kainic acid (KA) on the subcellular expression of PKC isozymes in the hippocampus (HPC) in the period preceding (0.5, 1.5, 12, and 24 h) a nd during (120 h) hippocampal necrosis using western blot analysis and PKC isozyme-specific antibodies. Before subcellular fractionation (cytosol + me mbrane), hippocampi were microdissected into "HPC" (fields CA1-CA3) and "de ntate gyrus" (DG; granule cells + hilus) regions. Four general patterns of alterations in PKC isozyme expression/distribution were observed following KA treatment. The first pattern was a relative stability in expression foll owing KA treatment and was most apparent for cytosol PKC alpha (HPC + DG) a nd membrane (HPC) and cytosol (DG) PKC beta II. The second pattern, observe d with PKC gamma and PKC epsilon, was characterized by an initial increase in expression in both membrane and cytosolic fractions before seizure activ ity (0.5 h) followed by a gradual decrease until significant reductions are observed by 120 h. The third pattern, exhibited by PKC delta, involved an apparent translocation, increasing in the membrane and decreasing in the cy tosol, followed by down-regulation in both fractions and subsequent recover y, The fourth pattern was observed with PKC zeta only and entailed a signif icant reduction in expression before and during limbic motor seizures follo wed by a dramatic fivefold increase in the membrane fraction during the per iod of hippocampal necrosis (120 h). Although these patterns did not segreg ate according to conventional PKC isozyme classifications, they do indicate dynamic isozyme-specific regulation by KA. The subcellular redistribution of PKC isozymes may contribute to the histopathological sequelae produced b y KA in the hippocampus and may model the pathogenesis associated with dise ases involving glutamate-induced neurotoxicity.