The primary culture of rat cerebellar neurons was used to study protein kinase C activity, intracellular variations in calcium concentration ([Ca(2+)]i), changes in the mitochondrial potential, and neuronal death during hyperstimulation of glutamate receptors and after 24-h incubation with phorbol ester. Prolonged exposure of neurons to glutamate (100 microM, 45 min) was followed by the development of delayed calcium dysregulation. Protein kinase C activity depended on the time of cell incubation with glutamate. Protein kinase C activity increased in response to application of glutamate for 15 min. However, protein kinase C activity decreased after 45-min exposure to glutamate and development of delayed calcium dysregulation. Protein kinase C activity was nearly undetected after 24-h preincubation of neurons with phorbol ester. Under these conditions, delayed calcium dysregulation developed more slowly and was observed in a smaller number of neurons. Neuronal death decreased to 2+/-1%. Our results suggest that protein kinase C plays an important role in death of neurons, which exhibit delayed calcium dysregulation during glutamate treatment.