Frequency response of alternating currents through the Staphylococcus aureus α‐hemolysin ion channel

Misakian, Martin; Kasianowicz, John J.; Robertson, Baldwin; Petersons, O.

doi:10.1002/bem.77.abs

Cited by 3 publications

(2 citation statements)

References 19 publications

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“…The presence of a large barrier is also inferred from the exponential form of current-voltage curves (Fig. 7), which differ from the near-linear current-voltage characteristics of water-filled, low-barrier aHL pores reconstituted in membranes (80). The combination of precise experimental results for the membrane thickness and specific capacitance is in quantitative accordance with a model in which Ab 1-42 -oligomers insert into the bilayer membrane, where they lead to domain formation.…”

Section: Discussionmentioning

confidence: 94%

Soluble Amyloid β-Oligomers Affect Dielectric Membrane Properties by Bilayer Insertion and Domain Formation: Implications for Cell Toxicity

Valinčius

Heinrich

Budvytytė

et al. 2008

Biophysical Journal

193

180

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It is well established that Alzheimer's amyloid beta-peptides reduce the membrane barrier to ion transport. The prevailing model ascribes the resulting interference with ion homeostasis to the formation of peptide pores across the bilayer. In this work, we examine the interaction of soluble prefibrillar amyloid beta (Abeta(1-42))-oligomers with bilayer models, observing also dramatic increases in ion current at micromolar peptide concentrations. We demonstrate that the Abeta-induced ion conductances across free-standing membranes and across substrate-supported "tethered" bilayers are quantitatively similar and depend on membrane composition. However, characteristic signatures of the molecular transport mechanism were distinctly different from ion transfer through water-filled pores, as shown by a quantitative comparison of the membrane response to Abeta-oligomers and to the bacterial toxin alpha-hemolysin. Neutron reflection from tethered membranes showed that Abeta-oligomers insert into the bilayer, affecting both membrane leaflets. By measuring the capacitance of peptide-free membranes, as well as their geometrical thicknesses, the dielectric constants in the aliphatic cores of 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1,2-diphytanoyl-sn-glycero-3-phosphocholine bilayers were determined to be epsilon = 2.8 and 2.2, respectively. The magnitude of the Abeta-induced increase in epsilon indicates that Abeta-oligomers affect membranes by inducing lateral heterogeneity in the bilayers, but an increase in the water content of the bilayers was not observed. The activation energy for Abeta-induced ion transport across the membrane is at least three times higher than that measured for membranes reconstituted with alpha-hemolysin pores, E(a) = 36.8 vs. 9.9 kJ/mol, indicating that the molecular mechanisms underlying both transport processes are fundamentally different. The Abeta-induced membrane conductance shows a nonlinear dependence on the peptide concentration in the membrane. Moreover, E(a) depends on peptide concentration. These observations suggest that cooperativity and/or conformational changes of the Abeta-oligomer particles upon transfer from the aqueous to the hydrocarbon environment play a prominent role in the interaction of the peptide with the membrane. A model in which Abeta-oligomers insert into the hydrophobic core of the membrane-where they lead to a local increase in epsilon and a concomitant reduction of the membrane barrier-describes the experimental data quantitatively.

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Section: Discussionmentioning

confidence: 94%

Soluble Amyloid β-Oligomers Affect Dielectric Membrane Properties by Bilayer Insertion and Domain Formation: Implications for Cell Toxicity

Valinčius

Heinrich

Budvytytė

et al. 2008

Biophysical Journal

193

180

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“…11 Other groups have inserted a single frequency into the voltage clamp protocol of different channel types and showed that the observed frequency response agreed with the expected response for some frequencies but not others. 12,13 Millonas and Hanck suggested the reason some frequencies did not produce the expected response is the presence of multiple rate constants in the Markov model. 12 Studies such as these, as well as others, have demonstrated that there are instances when ionic currents measured from ion channels while using impedance spectroscopy do not agree with the theoretical frequency response.…”

Section: Discussionmentioning

confidence: 99%

Recapitulation of an Ion Channel IV Curve Using Frequency Components

Rigby

Poelzing

2011

JoVE

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INTRODUCTION: Presently, there are no established methods to measure multiple ion channel types simultaneously and decompose the measured current into portions attributable to each channel type. This study demonstrates how impedance spectroscopy may be used to identify specific frequencies that highly correlate with the steady state current amplitude measured during voltage clamp experiments. The method involves inserting a noise function containing specific frequencies into the voltage step protocol. In the work presented, a model cell is used to demonstrate that no high correlations are introduced by the voltage clamp circuitry, and also that the noise function itself does not introduce any high correlations when no ion channels are present. This validation is necessary before the technique can be applied to preparations containing ion channels. The purpose of the protocol presented is to demonstrate how to characterize the frequency response of a single ion channel type to a noise function. Once specific frequencies have been identified in an individual channel type, they can be used to reproduce the steady state current voltage (IV) curve. Frequencies that highly correlate with one channel type and minimally correlate with other channel types may then be used to estimate the current contribution of multiple channel types measured simultaneously.

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