Chronic hypoxia inhibits Na+/Ca2+ exchanger expression in cortical astrocytes

Ca2+ signalling is central to many diverse functions of astrocytes. Of the numerous proteins involved in Ca2+ homeostasis, the Na+/Ca2+ exchanger is of particular importance in signalling regulation. We have shown that Ca2+ signaling is dramatically remodelled in astrocytes by periods of chronic hypoxia, in part by inhibition of Na+/Ca2+ exchanger. Here, we demonstrate that bepridil-sensitive Ca2+ extrusion (indicative of Na+/Ca2+ exchanger activity) is suppressed following 24 h hypoxia (2.5 or 1% O-2) owing to a loss of Na+/Ca2+ exchanger expression, as determined using immunocytochemistry and Western blots. Hypoxic Na+/Ca2+ exchanger I inhibition occurs at the level of transcription, as mRNA for Na+/Ca2+ exchanger I was significantly suppressed by hypoxia. Our results show hypoxia perturbs Ca2+ homeostasis in astrocytes via the suppression of Na+/Ca2+ exchanger I expression.