Abstract
Synthetic lipid membranes can display channel-like ion conduction events even in the absence of proteins. We show here that these events are voltage-gated with a quadratic voltage dependence as expected from electrostatic theory of capacitors. To this end, we recorded channel traces and current histograms in patch-experiments on lipid membranes. We derived a theoretical current-voltage relationship for pores in lipid membranes that describes the experimental data very well when assuming an asymmetric membrane. We determined the equilibrium constant between closed and open state and the open probability as a function of voltage. The voltage-dependence of the lipid pores is found comparable to that of protein channels. Lifetime distributions of open and closed events indicate that the channel open distribution does not follow exponential statistics but rather power law behavior for long open times.
Highlights
Synthetic lipid bilayers can display channel-like conduction events through pores in the bilayer [1]
The solid line represents a fit to eq 6 yielding V0~{110 mV, cp~6:62 nS, DG0~5:2 kJ/mol, and a~{248 kJ/mol:V2). This fit reproduces the experimental current-voltage profile very well. Such an outward rectified I–V curve for a synthetic membrane was already shown in [28] where it was analyzed with an Eyring transition state model that is very commonly used in the protein channel field
Our results show that fitting the open-time probability distribution functions (PDF) with a biexponential function as commonly done for protein channels may be quite misleading
Summary
Synthetic lipid bilayers can display channel-like conduction events through pores in the bilayer [1] This finding was first reported by Yafuso and collaborators [2] on oxidized cholesterol membranes. In various studies in the recent decade, Colombini and collaborators reported that ceramide lipids may form pores in membranes with channel-like conduction appearance [11,12,13,14,15,16]. The authors propose that ceramide channels are stable structures (comparable to a porin, see tentative structure in [17]) The conductances of such pores are much larger (several nS), the lifetimes are longer (several seconds to minutes) and it is uncertain whether ceramide-channels possess the same characteristics as other lipid pores, which rather resemble fluctuations in membrane density with amplitudes and lifetimes given by the thermal fluctuations of the lipid matrix (see below)
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