Effect of Synthetic Aβ Peptide Oligomers and Fluorinated Solvents on Kv1.3 Channel Properties and Membrane Conductance

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.

Non-pretreated O-acyl isopeptide of amyloid β peptide 1–42 is monomeric with a random coil structure but starts to aggregate in a concentration-dependent manner

“…Use of this substitution could enable benign applications of isoAb42, because TFA is known to sometimes affect cellular assays or in vivo assays. 14,32 In summary, we confirmed that isoAb42 without pretreatment has a monomeric and random coil form under acidic conditions at 40 lM based on the data from analytical ultracentrifugation and CD spectra. This nature was not altered by the conversion of counter anion from TFA to HCl.…”

“…7,8,[10][11][12] Also, any residual organic solvent may affect the subsequent assays. 13,14 Moreover, the obtained monomeric Ab may regenerate aggregates because of its inherent aggregative nature. To overcome these obstacles, an 'O-acyl isopeptide method' was tried in 2004.…”

Intracellular soluble α‐synuclein oligomers reduce pyramidal cell excitability

“…For example, it has been reported that there is cross‐talk between αSyn and voltage‐gated K + channels (Mironov, ) and β amyloid oligomers can change the activity of Kv 1.3 channels, whereas monomers have no effect (Lioudyno et al . ). The recruitment of voltage‐gated K + channels to the membrane or changes in K + channel activation would be consistent with the observed speeding of action potential repolarization.…”

Potassium Channel Kv1.3 Is Highly Expressed by Microglia in Human Alzheimer's Disease

“…This observation creates the potential for Aβ to interact with Kv1.3 channels. Interestingly, Aβ 1–42 oligomers, but not soluble Aβ, accelerate the activation and inactivation kinetics of Kv1.3 channels in lipid bilayers without altering channel conductance [34]. Rapid activation and inactivation of Kv1.3 channels could alter calcium fluxes in neurons and microglia but the relevance of this potential Kv1.3-Aβ interaction has not been evaluated.…”