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

Abstract

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 μM) increased PKC activity, while exposure to a higher dose (10 μM) led to decreased PKC activity. Additionally, in normal extracellular medium, low concentration of Pb 2+ (0.01 μM) stimulated increase in cytosolic free calcium while the higher concentrations of Pb 2+ (10 μM) did not. However, the effect of low dose Pb 2+ (0.01 μM) 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 μM) produced reactive oxygen species (ROS) dose dependently over the period of 24 h. Pb 2+-induced ROS were potentiated in the presence of 500 μM 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 μM). It is concluded that, in Pb-induced cytotoxicty, modulation of PKC and intracellular calcium play significant roles in augmenting glutamate receptor mediated oxidative species formation and subsequent cell death.