Abstract
The impact of synthetic amyloid β (1–42) (Aβ1–42) oligomers on biophysical properties of voltage-gated potassium channels Kv 1.3 and lipid bilayer membranes (BLMs) was quantified for protocols using hexafluoroisopropanol (HFIP) or sodium hydroxide (NaOH) as solvents prior to initiating the oligomer formation. Regardless of the solvent used Aβ1–42 samples contained oligomers that reacted with the conformation-specific antibodies A11 and OC and had similar size distributions as determined by dynamic light scattering. Patch-clamp recordings of the potassium currents showed that synthetic Aβ1–42 oligomers accelerate the activation and inactivation kinetics of Kv 1.3 current with no significant effect on current amplitude. In contrast to oligomeric samples, freshly prepared, presumably monomeric, Aβ1–42 solutions had no effect on Kv 1.3 channel properties. Aβ1–42 oligomers had no effect on the steady-state current (at −80 mV) recorded from Kv 1.3-expressing cells but increased the conductance of artificial BLMs in a dose-dependent fashion. Formation of amyloid channels, however, was not observed due to conditions of the experiments. To exclude the effects of HFIP (used to dissolve lyophilized Aβ1–42 peptide), and trifluoroacetic acid (TFA) (used during Aβ1–42 synthesis), we determined concentrations of these fluorinated compounds in the stock Aβ1–42 solutions by 19F NMR. After extensive evaporation, the concentration of HFIP in the 100× stock Aβ1–42 solutions was ∼1.7 μM. The concentration of residual TFA in the 70× stock Aβ1–42 solutions was ∼20 μM. Even at the stock concentrations neither HFIP nor TFA alone had any effect on potassium currents or BLMs. The Aβ1–42 oligomers prepared with HFIP as solvent, however, were more potent in the electrophysiological tests, suggesting that fluorinated compounds, such as HFIP or structurally-related inhalational anesthetics, may affect Aβ1–42 aggregation and potentially enhance ability of oligomers to modulate voltage-gated ion channels and biological membrane properties.
Highlights
Complex mechanisms that may contribute to Alzheimer’s disease (AD) involve genetic and environmental factors [1,2] that under some, often unknown, conditions converge to initiate the onset of the neurodegeneration
Because amyloid b (Ab) has been associated with characteristic pathological changes, these findings are in the center of the debate whether the membrane effects of Ab oligomers are at the core of AD etiology
To compare the sizes and size distributions of Ab1–42 aggregates prepared by different protocols at similar time points after initiating oligomer formation, we used dynamic light scattering (DLS)
Summary
Complex mechanisms that may contribute to Alzheimer’s disease (AD) involve genetic and environmental factors [1,2] that under some, often unknown, conditions converge to initiate the onset of the neurodegeneration. The level of OC-stained fibrillar oligomers in the multiple brain regions correlates with the level of cognitive decline and other neuropathological hallmarks of Alzheimer’s disease [8]. Multiple mechanisms by which oligomers cause calcium dysregulation, synaptic dysfunction, and neuronal cell death have been proposed These include amyloid interactions with cellular membranes [11,12,13], the amyloid channel hypothesis [14,15], amyloid effects on ion channels [16,17,18,19,20] and on neurotransmitter receptors [21,22,23,24]. Because Ab has been associated with characteristic pathological changes, these findings are in the center of the debate whether the membrane effects of Ab oligomers are at the core of AD etiology
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