Protein Kinase C in Rat Brain Is Altered by Developmental Lead Exposure

The absence of learning-related redistribution of hippocampal protein kinase C (PKC) has been correlated with impairment of learning performance induced by developmental lead (Pb) exposure. This study was designed to examine whether the properties of brain PKC are altered by chronic Pb exposure during development. Two-tenth percent Pb acetate was administered to pregnant and lactating dams and then administered to weanlings in drinking water until postnatal day (PN) 56. Effects of Pb on translocation of PKC were studied in brain slices prepared from hippocampus. When the slices were treated with 0.33 M phorbol-12, 13-dibutyrate (PDBu) for 15 min, a significant increase in PKC activity was observed in the membrane fraction of hippocampal slices from Pb-exposed rats, suggesting that chronic Pb exposure potentiates PDBu-activated PKC translocation. Data obtained from saturation binding assays in the frontal cortices of Pb-exposed rats showed a decrease in the dissociation constant (K_D) in both membrane and cytosolic PKC. A decrease in the total binding sites (B_max) of ³H]PDBu binding was only observed in membrane PKC. Furthermore, developmental Pb exposure decreased PKC-, but not PKC-, -II, and - in the membrane fraction of the hippocampus and the frontal cortex. These results indicate that chronic Pb exposure during development increases phorbol ester binding affinity, enhances phorbol ester-induced translocation of PKC, and down-regulates membrane PKC, mainly PKC-.