Amyloid-beta 1–42 peptide inhibits Na+/K+ ATPase activity. Purified cerebral Na+/K+ ATPase was pre-incubated with vehicle or Aβ 1–42, and enzyme activity percentages of the vehicle (20 μmols Pi/mg protein/hour) are presented (mean ± SEM). "◊" indicates the values for the soluble (DMSO+water) Aβ suspension. "○" indicates the values for the fibrillar (DMSO+neutralized HCl) Aβ suspension. At the highest concentrations, the soluble preparation dramatically reduces Na+/K+ ATPase activity compared to both vehicle and the fibrillar Aβ preparation. * (p < 0.05) and *** (p < 0.001) indicates significant differences between Aβ and vehicle alone when measured by one-way ANOVA.