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1 Academic Unit of Child Health, University of Manchester, St. Mary's Hospital, Manchester M13 0JH and 2 School of Biological Sciences, University of Manchester, Manchester M13 9PL, United Kingdom
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 86Rb as a trace marker. Intracellular Ca2+ ([Ca2+]i) was examined by microfluorometry using fura 2. [ATP]o significantly increased 86Rb 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 86Rb efflux in both groups as did application of 150 µM GdCl3. [ATP]o significantly increased [Ca2+]i in both groups of cells. The response was reduced by removing [Ca2+]o and applying 150 µM GdCl3. For both 86Rb efflux and microfluorometry experiments, the response to [ATP]o was more dependent on [Ca2+]o in 66-h cells compared with 18-h cells (~70% 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.
intermediate calcium-activated potassium channel; calcium entry; human placenta
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