Amyloid ␤ protein (A␤P) forms senile plaques in the brain of the patients with Alzheimer's disease. The early-onset AD has been correlated with an increased level of 42-residue A␤P (A␤P 1-42 ). However, very little is known about the role of A␤P 1-42 in such pathology. We have examined the activity of A␤P 1-42 reconstituted in phospholipid vesicles. Vesicles reconstituted with A␤P show strong immunofluorescence labeling with an antibody raised against an extracellular domain of A␤P suggesting

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... e incorporation of A␤P peptide in the vesicular membrane. Vesicles reconstituted with A␤P showed a significant level of 45 Ca 2؉ uptake. The 45 Ca 2؉ uptake was inhibited by (i) a monoclonal antibody raised against the N-terminal region of A␤P, (ii) Tris, and (iii) Zn 2؉ . However, reducing agents Trolox and dithiothreitol did not inhibit the 45 Ca 2؉ uptake, indicating that the oxidation of A␤P or its surrounding lipid molecules is not directly involved in the A␤P-mediated Ca 2؉ uptake. An atomic force microscope was used to image the structure and physical properties of these vesicles. Vesicles ranged from 0.5 to 1 m in diameter. The stiffness of the A␤P-containing vesicles was significantly higher in the presence of calcium. The stiffness change was prevented in the presence of zinc, Tris, and anti-A␤P antibody but not in the presence of Trolox and dithiothreitol. Thus the stiffness change is consistent with the vesicular uptake of Ca 2؉ . These findings provide biochemical and structural evidence that A␤P 1-42 forms calcium-permeable channels and thus may induce cellular toxicity by regulating the calcium homeostasis in Alzheimer's disease.