Contribution of protein kinase C and glutamate in Pb2+-induced cytotoxicity

Activation of protein kinase C (PKC) plays an important role in lead (Pb2+) -induced cytotoxicity. The effects of low dose exposure to Pb2+ on cytosoli c free calcium (Ca2+), PKC activity and mechanisms involved in cell death w ere studied in PC12 cells. Exposure of PC12 cells to low dose Pb2+ (0.01 mu M) increased PKC activity, while exposure to a higher dose (10 mu M) led t o decreased PKC activity. Additionally, in normal extracellular medium, low concentration of Pb2+ (0.01 mu M) stimulated increase in cytosolic free ca lcium while the higher concentrations of Pb2+ (10 mu M) did not, However, t he effect of low dose Pb2+ (0.01 mu M) was blocked by removing Ca2+ from ex ternal medium. The role of Pb2+ -induced changes in PKC activity and its re lationship to oxidative stress and related cytotoxicity was also studied. P b2+ alone (0.01-10 mu M) produced reactive oxygen species (ROS) dose depend ently over the period of 24 h. Pb2+-induccd ROS were potentiated in the pre sence of 500 mu M glutamate. Furthermore, a correlation was observed betwee n ROS generation and the levels of cytotoxicity, which was observed after 2 4 h exposures to Pb2+ by trypan blue method, and the cytotoxicity was enhan ced by glutamate co-treatment. Pb2+-induced cell death was blocked partiall y by staurosporine (PKC inhibitor. 100 nM) and NMDA antagonist, MK-801 (1 m u M). it is concluded that, in Pb-induced cytotoxicty, modulation of PKC an d intracellular calcium play significant roles in augmenting glutamate rece ptor mediated oxidative species formation and subsequent cell death. (C) 20 00 Elsevier Science Ireland Ltd. All rights reserved.