Complexity of depolarization-mediated ERK phosphorylation in cerebellar granule cells in primary cultures

We previously showed that cultured mouse cerebellar granule cells during incubation in glutamine-replete medium respond to 45 mM [K(+)](e) after 20 and 60 min incubation with extracellular-signal regulated kinase 1 and 2 (ERK(1/2)) phosphorylation which is mainly, but probably not exclusively, secondary to glutamate release and transactivation of epidermal growth factor (EGF) receptors. In the present study the response after 20 min was shown to be abolished by protein kinase C (PKC) inhibition, whereas that at 60 min was PKC-independent. Addition of 50 microM glutamate to the cells caused ERK(1/2) phosphorylation already after 5 min most of which was sensitive to PKC inhibition although a minor part was PKC inhibition-resistant. Exposure to [K(+)](e) during incubation in glutamine-depleted medium caused no stimulated release of glutamate but a transactivation-independent ERK(1/2) phosphorylation at 20 and 60 min. The response at 20 min was insensitive to PKC inhibition. The potential importance of these complex responses for synaptic plasticity is discussed.