Contribution of protein kinase C and glutamate in Pb(2+)-induced cytotoxicity.

Activation of protein kinase C (PKC) plays an important role in lead (Pb(2+))-induced cytotoxicity. The effects of low dose exposure to Pb(2+) on cytosolic free calcium (Ca(2+)), PKC activity and mechanisms involved in cell death were studied in PC12 cells. Exposure of PC12 cells to low dose Pb(2+) (0.01 microM) increased PKC activity, while exposure to a higher dose (10 microM) led to decreased PKC activity. Additionally, in normal extracellular medium, low concentration of Pb(2+) (0.01 microM) stimulated increase in cytosolic free calcium while the higher concentrations of Pb(2+) (10 microM) did not. However, the effect of low dose Pb(2+) (0.01 microM) was blocked by removing Ca(2+) from external medium. The role of Pb(2+)-induced changes in PKC activity and its relationship to oxidative stress and related cytotoxicity was also studied. Pb(2+) alone (0.01-10 microM) produced reactive oxygen species (ROS) dose dependently over the period of 24 h. Pb(2+)-induced ROS were potentiated in the presence of 500 microM glutamate. Furthermore, a correlation was observed between ROS generation and the levels of cytotoxicity, which was observed after 24 h exposures to Pb(2+) by trypan blue method, and the cytotoxicity was enhanced by glutamate co-treatment. Pb(2+)-induced cell death was blocked partially by staurosporine (PKC inhibitor, 100 nM) and NMDA antagonist, MK-801 (1 microM). It is concluded that, in Pb-induced cytotoxicity, modulation of PKC and intracellular calcium play significant roles in augmenting glutamate receptor mediated oxidative species formation and subsequent cell death.