A virtual instrumentation based protocol for the automated implementation of the inner field compensation method

Abstract

Abstract:One influential parameter which mediates interactions between many types of molecules and biological membranes stems from the lumped contributions of the transmembrane potential, dipole potential and the difference in the surface potentials on both sides of a membrane. With relevance to cell physiology, such electrical features of a biomembrane are prone to undergoing changes as a result of interactions with the aqueous surrounding. Among the most useful tools devoted to exploring changes of electrical parameters of a lipid membrane induced by certain extracellular ions, lipid composition, and embedded membrane peptides and proteins, are spectroscopic imaging and the inner field compensation (IFC) method. In this work we layout the principles of a fully computerized version of the IFC method, which makes it more readily available to users. As a direct application, we deployed this improved version of the IFC method to timeresolve changes induced by alamethicin monomers upon membrane dipole potential, following their aggregation within an artificial lipid membrane. Intriguingly, even prior crossing the membrane core, the membrane-bound alamethicin monomers are shown to significantly increase the dipole potential of the monolayer they reside in. Such data further emphasize the yet less-explored interplay between membrane-based protein and peptides, and the membrane dipole potential.

Teaching an old dog new tricks: A lipid membrane‐based electric immunosensor for real‐time probing of the spike S1 protein subunit from SARS‐CoV‐2

“…As illustrated in Figure 1A and demonstrated previously [18,19], in assessing the physical response of a lipid membrane to an applied potential difference (Figure 1B), two considerations are crucial: (i) due to electrostriction effects on an equivalent "elastic" capacitor that models to a first approximation a reconstituted lipid membrane, the If for a such model lipid membrane, the externally applied potential difference consists of a constant term (u 0 ) and a sinusoidal component with amplitude (u 1 ) and pulsation (ω) (ΔV ext = u 0 + u 1 sin(𝜔t)), by virtue of elementary circuit analysis, it follows that the resulting time-dependent capacitive current (I C (t)) embodies three harmonics of the fundamental pulsation (ω) (Supporting Information). For our analysis we focused solely on the second harmonic isolated from the power-spectra of the capacitive current (Figure 2A), which in the time-domain and with the notations employed above writes:…”

“…As illustrated in Figure 1A and demonstrated previously [18, 19], in assessing the physical response of a lipid membrane to an applied potential difference (Figure 1B), two considerations are crucial: (i) due to electrostriction effects on an equivalent “elastic” capacitor that models to a first approximation a reconstituted lipid membrane, the membrane capacitance ( C ) depends quadratically upon the sensed voltage difference (Δ V H ) across its hydrophobic core ($$C\ = {C_0}( {1 + \alpha \Delta {V_{\rm{H}}}^2} )$$ ( C 0 represents for the minimum value of the membrane capacitance at Δ V H = 0 and α [ V −2 ] is a constant (Supporting Information); (ii) the actual Δ V H embodies three main contributions, arising from the externally applied potential difference across the lipid membrane (Δ V ext ), the difference on the lipid membrane surface potentials ( V S ) measured on both sides of the membrane, and respectively the difference in the membrane dipole potentials (Δ V D ) [20–23], as measured between the cis and trans monolayers of the membrane.…”

“…All experiments were performed at a room temperature of ∼25°C, and all protein stock solutions were kept at −20°C when not used. The working principle used for the automated real‐time monitoring and evaluating of the capacitive current through the lipid bilayer was based on the well‐established inner field compensation (IFC) method, as previously described [ 18 ]. Briefly, we constructed a virtual instrument to collect the capacitive current via Ag/AgCl electrodes coupled with a Multiclamp 700B computer‐controlled amplifier or Axopatch 200B instrument (Molecular Devices, USA).…”

Phlorizin- and 6-Ketocholestanol-Mediated Antagonistic Modulation of Alamethicin Activity in Phospholipid Planar Membranes

“…To only monitor how the difference in the dipole potential of the membrane unfolds in time as a result of specific interactions with phlorizin molecules, the dc bias of the applied voltage signal to the membrane ( U = U 0 + U 1 sin (2πυ t ), ν = 220 Hz, U 1 = 50 mV) was kept constant (usually zero, for symmetrical phosphatidylcholine-based membranes), and the time-evolution of the amplitude of the second harmonic component (at the 440 Hz) was recorded . In such experiments, alamethicin monomers were excluded from the interaction with the lipid membrane.…”