Objective: Acidification of extracellular pH has been shown to trigger specific Ca2+ responses in neurons. We examined the role of the Ca2+- permeable acid-sensing ion channel 1a (ASIC1a) in regulating acidosis-dependent Ca2+ signaling. Methods: For fluorescence imaging of [Ca2+]i, murine cortex neurons or transfected CHO cells were loaded with the Ca2+-sensitive indicator fura-2. In preconditioning experiments, cortical neurons or CHO cells were exposed to prolonged acidosis (pH 6.0) for 1, 6, and 12h prior to [Ca2+]i measurement. Results: Cortex neurons responded to low pH (pH 6.5 to pH 5.0) with initial but transient [Ca2+]i peaks. Application of amiloride and PcTx1, a specific blocker of ASIC1a, was used to determine the contribution of ASIC1a to preconditioning by acidosis. Furthermore, we investigated the role of ASIC1a in regulating the [Ca2+]i-dependent transcription factor NFAT (nuclear factor of activated T- cells), which has been implicated in neuronal survival during acidosis. To characterize NFAT regulation during acidosis, we transfected CHO cells with a plasmid encoding NFAT4 fused with a green fluorescent protein. Monitoring GFP- fluorescence, we found prolonged acidosis to induce nuclear import of NFAT4 in CHO cells co- expressing ASIC1a. Conclusion: Our findings indicate that activation of ASIC1a contributes to pH-dependent modulation of intracellular Ca2+ signaling.