Abstract
In this study, a lipid bilayer membrane model was used, in which the bilayer is tethered to a solid substrate with molecular tethers. The V–I characteristics of the lipid bilayers were found to be non-linear which suggests the presence of pores that are voltage-dependent. At high applied voltages, the conductance reached a limiting value, presumably indicating a limit on the maximum pore size. A decrease in the spacing between tethers (increasing tether density) caused a decrease in the membrane’s conductance at high applied voltage, which is consistent with the maximum pore size being determined by the spacing between the tethers. The inclusion of 10 M% cholesterol within the membrane lipid caused a decrease in the membrane conductance. However, the inclusion of higher levels of cholesterol increased the membrane conductance.
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HA wishes to gratefully acknowledge the award of a University of Sydney Post Graduate Research Scholarship
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Appendix
Appendix
In this study, the V–I measurements were recorded by applying high frequency (50 Hz) voltage ramps. The application of potential ramps of high frequency was important to avoid the non-linearities that otherwise result from capacitive coupling of the membrane to the gold electrodes. Figure 11 shows an equivalent circuit of a tethered lipid membrane connected to a triangular voltage ramped source. The response of this circuit was simulated using 5 Spice Analysis 2.0 software and shown in Figs. 12, 13 and 14. Figures 12 and 13 show that when the applied potential triangular ramps (TPdv1) were fast enough (50 Hz or 10 Hz) with a time course limited to few milliseconds; the membrane response voltage (TPdv2) and the current (TPi1) charging through the membrane were linear and matched the linear properties of the applied voltage. However, Fig. 13 shows that when the applied triangular voltage ramps (TPdv1) were slower (1 Hz) the membrane response voltage (TPdv2) as well as the current (TPi1) were no longer linear, because of the effect of the capacitive charging of the gold electrode-solution/tethers.
If the ramps are fast enough therefore it is possible to measure the V–I characteristics of the membrane, despite the fact that the gold electrode is a DC blocking electrode.
Equivalent circuit of tBLM. For an electrode area of 2.1 mm2, the capacitances of the gold counter electrode, the tethering gold surface and the tBLM respectively are 1500 nF, 150 nF and 15 nF. A 1 V- triangular ramped voltage was applied across the tethered membranes; where TPdv1 is the applied triangular ramped voltage waveform, TPdv2 is the membrane response voltage and TPi1 is the charging current through the membrane
Solution of the equivalent circuit of tethered lipid membrane (shown in Fig. 11) simulated by 5 Spice software when a 1 V–50 Hz triangular voltage ramps were applied. Full line: current, dashed line: voltage applied to the system, Dotted & Dashed line: voltage across membrane
Solution of the equivalent circuit of tethered lipid membrane (shown in Fig. 11) simulated by 5 Spice software when a 1 V–10 Hz triangular voltage ramps were applied. Full line: current, dashed line: voltage applied to the system, dotted and dashed line: voltage across membrane
Solution of the equivalent circuit of tethered lipid membrane (shown in Fig. 11) simulated by 5 Spice software when a 1 V–1 Hz triangular voltage ramps were applied. Full line: current, dashed line: voltage applied to the system, dotted and dashed line: voltage across membrane
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Alobeedallah, H., Cornell, B. & Coster, H. The Effect of Cholesterol on the Voltage–Current Characteristics of Tethered Lipid Membranes. J Membrane Biol 253, 319–330 (2020). https://doi.org/10.1007/s00232-020-00130-5
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DOI: https://doi.org/10.1007/s00232-020-00130-5