ATP-stimulated Ca2+-activated K+ efflux pathway and differentiation of human placental cytotrophoblast cells

The aim of this study was to determine whether extracellular ATP ([ATP](o)) stimulated a Ca2+-activated K+ efflux in trophoblast cells that was dependent on extracellular Ca2+ ([Ca2+](o)). Cytotrophoblast cells, isolated from human placenta, were examined following 18 h (relatively undifferentiated) and 66 h (multinucleate cells) of culture. Potassium efflux was measured using Rb-86 as a trace marker. Intracellular Ca2+ ([Ca2+](o)) was examined by microfluorometry using fura 2. [ATP] o significantly increased Rb-86 efflux to a peak that declined to control (18-h cells) or an elevated plateau (66-h cells) and was inhibited by 100 nM charybdotoxin. Removing [Ca2+](o) significantly reduced Rb-86 efflux in both groups as did application of 150 muM GdCl3. [ATP](o) significantly increased [Ca2+](i) in both groups of cells. The response was reduced by removing [Ca2+](o) and applying 150 muM GdCl3. For both Rb-86 efflux and microfluorometry experiments, the response to [ATP] o was more dependent on [Ca2+](o) in 66-h cells compared with 18-h cells (similar to70% greater). Cytotrophoblast cells exhibit an [ATP](o)-stimulated Ca2+-activated K+ efflux. The dependency of this pathway on [Ca2+](o) is greater in the 66-h multinucleate syncytiotrophoblast- like cells, suggesting that the mechanism for Ca2+ entry may be altered during differentiation of trophoblast cells.