Abstract

Oligomeric forms of Aβ peptides are implicated in Alzheimer's disease and disrupt membrane integrity, leading to cytosolic calcium elevation. Proposed mechanisms by which Aβ mediates its effects include lipid destabilization, activation of native membrane channels, and aggregation of Aβ into Ca2+-permeable pores. We distinguished between these using total internal reflection fluorescence microscopy to image Ca2+ influx in Xenopus laevis oocytes. Aβ1-42 oligomers evoked single-channel Ca2+ fluorescence transients, which resembled those from classical ion channels but which were not attributable to endogenous oocyte channels. SCCaFTs displayed widely variable open probabilities and stepwise transitions among multiple amplitude levels reminiscent of subconductance levels of ion channels. The proportion of high Po, large amplitude SCCaFTs grew with time, suggesting that continued oligomer aggregation results in the formation of highly toxic pores. We conclude that formation of intrinsic Ca2+-permeable membrane pores is a major pathological mechanism in AD and introduce TIRF imaging for massively parallel single-channel studies of the incorporation, assembly, and properties of amyloidogenic oligomers.