EFFECTS OF PHORBOL ESTER ON INTRACELLULAR CA2+ AND MEMBRANE CURRENTS IN CULTURED HUMAN MICROGLIA

The effects of protein kinase C (PKC) activation by phorbol ester on i ntracellular Ca2+ concentration ([Ca2+](i)) and membrane currents in h uman microglia grown in culture were investigated. Treatment of microg lia with phorbol myristate acetate (PMA) resulted in a large increase in [Ca2+](i) in cells loaded with fura-2. The increased levels of [Ca2 +](i) were not altered following removal of the phorbol ester. In Ca2-free medium, application of PMA did not increase [Ca2+](i). In additi on, PMA application in standard Ca2+-solution containing lanthanum (1. 8 mM) had no effect on the microglial response to PMA, suggesting that the phorbol ester actions were due to transmembrane influx of Ca2+ bu t not through voltage-gated Ca2+ channels, Whole-cell patch clamp meas urements demonstrated that PMA potentiated an outward K+ current and i nhibited an inward rectifier K+ current. This study is the first demon stration that PKC activation by phorbol eater leads to increased intra cellular [Ca2+] and changes in membrane currents in human microglia.