Amyloid β-peptides inhibit Na/K-ATPase: tissue slices versus primary cultures

Abstract

Aβ 1-40 (20 μM) has been reported to selectively inhibit Na +/K +-ATPase activity in rat primary hippocampal cultures after 2–6 days of exposure [10]. We expanded these studies to include Aβ’s effects on Na +/K +-ATPase activity in rat primary cortical cultures and hippocampal slices, and we correlated these effects with estimates of cell survival in rat brain primary cultures. Using optimized assay conditions, a 5-day exposure to 50 μM Aβ 25-35, 20 μM Aβ 1-40, and 20 μM Aβ 1-42 decreased Na +/K +-ATPase activity in rat primary cortical cultures 66%, 60%, and 22%, respectively. Aβ 25-35 (50 μM) at 24 h was the only condition that caused inhibition of Na +/K +-ATPase activity in the absence of cell death, defined as an extracellular shift in the localization of the cytoplasmic enzyme lactate dehydrogenase (LDH). We also found that hippocampal slices were sensitive to Aβ, exhibiting a 40–60% reduction in membrane Na +/K +-ATPase activity when exposed to 1–30 nM of Aβ 1-40 for 60 min. This inhibition was not readily reversible, as it withstood homogenization and repeated dilution and centrifugation. Additionally, this inhibition occurred only after amyloid incubation with intact hippocampal slices, not with disrupted membranes. The inhibition of Na +/K +-ATPase in brain slices by physiological, low nM concentrations of Aβ 1-40 is consistent with effects on neurotransmitter release and intrasynaptosomal calcium responses [4,7].