PSEN1 and amyloidosis: Using a sensitive colorimetric assay to measure activity of Na+/K+ ATPase modified from Ellis et al. [23], we were able to demonstrate that in the APP+PS1 hippocampus, the specific activity of ouabain-sensitive ATPase was significantly reduced (figure 1B) while Na+/K+ ATPase activity in the amyloid-free cerebellum remained unperturbed with respect to genotype.