RESUMO
A plethora of protein kinase C (PKC) isoforms play important roles in regulating synaptic plasticity and neurotransmitter release. Even though, most PKC isoforms are involved in Pb-induced neuronal toxicity, its mechanism is still unclear. The current study addresses the effect of Pb on PKC isoforms in different regions of the developing rat brain. Sprague-Dawley (SD) pregnant rats were exposed to 0.1% Pb as lead acetate dissolved in distilled deionized water (DDW) from gestation day 6 through 21 postnatal day (PND). Control rats were allowed to drink DDW. Pups were sacrificed on PND 1, 5, 10 and 45. Rat brain was immediately excised and separated into the brain stem (BS), the cerebellum (CB), the hippocampus (HC) and the frontal cortex (FC). The Pb level in different regions of the brain was determined using an analytical graphite tube atomizer (Varian). Typical PKC (alpha, beta, gamma), novel PKC (epsilon) and atypical PKC (mu) in the above brain regions were enriched by immunoprecipitation and later were assayed by Western blotting. The total, calcium-dependent and -independent PKC activities were determined by the radioactivity of total gamma-32P transferred to histone. The results indicated that on PND 1, Pb reduced the PKC-gamma protein in HC and FC, whereas on PND 5 the proteins of PKC isoforms (alpha, beta, gamma, epsilon, mu) in HC and FC were significantly reduced. These reductions in PKC proteins were higher in membrane fractions than in cytosolic fractions. On PND 10, Pb reduced all PKC isoforms. However, on PND 45, Pb had no significant effect on all PKC isoforms except epsilon. Pb inhibited the total PKC activity by 70% on PND 1 and 5, the bulk of these PKC activities were calcium-dependent. The results suggest that during early stages of the rat brain development, Pb exposure decreased PKC activities and also reduced PKC isoforms including PKC-gamma and epsilon which are reported to have roles in the memory formation and long-term potentiation (LTP).
