CALMODULIN MODULATES MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION IN RESPONSE TO MEMBRANE DEPOLARIZATION IN PC12 CELLS

In the absence of neurotrophic factors, chronic depolarization of plas ma membrane has been shown to maintain several populations of primary neurons in culture. We report that in the PC12 cell line, depolarizati on causes Ca2+ influx through voltage-gated Ca2+ channels, which is ab le to stimulate extracellular-regulated kinase (ERK) activity. We stud ied which mediators were responsible for ERK activation resulting from increased levels of Ca2+ in the cytoplasm and found that calmodulin w as involved in this process. The addition of W13, a calmodulin inhibit or, to the culture medium, prevented ERK activation when PC12 cells we re depolarized. In addition, we show that high K+ treatment did not in duce Trk A phosphorylation, thus excluding the possibility of Ca2+ ope rating through this receptor to activate the ERK signal transduction p athway. Moreover, although high K+ treatment is able to phosphorylate the epidermal growth factor receptor (EGFR) and thus to activate the E RK signal transduction pathway, we demonstrate that W13 did not alter the state of EGFR phosphorylation in conditions that almost completely blocked ERK activation. These data suggest that calmodulin mediates E RK activation induced by increases in intracellular Ca2+ concentration in PC12 cells by a mechanism that seems to be independent of Trk A an d EGFR activation.