Concentration-dependent induction of NFAT-driven reporter gene expression by extracellular ATP. PC12-NFAT-Luc cells were treated with varying concentrations of ATP for 3 h before lysis. Luciferase activities were normalised to the maximum induction obtained with 300 μM ATP. The graph presents means ± SD of n = 3 independent experiments. Nonlinear curve-fitting yielded EC50 = 78 μM ATP (95% confidence interval 62-95 μM ATP).