Voltage Gated Lipid Ion Channels

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

The Emotional Impact of Pictures when Crowdfunding for Healthcare: An Experimental Study

This study investigates how visual stimuli influence cancer-related charitable online giving. Particularly, the study investigates how different types of crowdfunding campaign pictures affect donors’ decision to contribute to specific campaigns. We gathered crowdfunding campaigns from GoFundMe and divided them according to the main picture used in each campaign, i.e., cancer-related pictures vs. non-cancer-related pictures and pictures of individuals vs. pictures of groups. We then conducted an online experiment and a laboratory experiment using physiological measures. The results from the experiments show that cancer-related pictures receive more money and more immediate attention and arousal than non-cancer-related pictures. Furthermore, group pictures receive more money and more total attention than individual pictures. The physiological measures from the laboratory experiment provide valuable knowledge about the underlying emotional mechanisms involved in the donation process

Comparing ion conductance recordings of synthetic lipid bilayers with cell membranes containing TRP channels

In this article we compare electrical conductance events from single channel recordings of three TRP channel proteins (TRPA1, TRPM2 and TRPM8) expressed in human embryonic kidney cells with channel events recorded on synthetic lipid membranes close to melting transitions. Ion channels from the TRP family are involved in a variety of sensory processes including thermo- and mechano-reception. Synthetic lipid membranes close to phase transitions display channel-like events that respond to stimuli related to changes in intensive thermodynamic variables such as pressure and temperature. TRP channel activity is characterized by typical patterns of current events dependent on the type of protein expressed. Synthetic lipid bilayers show a wide spectrum of electrical phenomena that are considered typical for the activity of protein ion channels. We find unitary currents, burst behavior, flickering, multistep-conductances, and spikes behavior in both preparations. Moreover, we report conductances and lifetimes for lipid channels as described for protein channels. Non-linear and asymmetric current-voltage relationships are seen in both systems. Without further knowledge of the recording conditions, no easy decision can be made whether short current traces originate from a channel protein or from a pure lipid membraneComment: 13 pages, 9 Figure

The temperature dependence of lipid membrane permeability, its quantized nature, and the influence of anesthetics

We investigate the permeability of lipid membranes for fluorescence dyes and ions. We find that permeability reaches a maximum close to the chain melting transition of the membranes. Close to transitions, fluctuations in area and compressibility are high, leading to an increased likelihood of spontaneous lipid pore formation. Fluorescence Correlation Spectroscopy (FCS) reveals the permeability for rhodamine dyes across 100 nm vesicles. Using FCS, we find that the permeability of vesicle membranes for fluorescence dyes is within error proportional to the excess heat capacity. To estimate defect size we measure the conductance of solvent-free planar lipid bilayer. Microscopically, we show that permeation events appear as quantized current events. Further, we demonstrate that anesthetics lead to a change in membrane permeability that can be predicted from their effect on heat capacity profiles. Depending on temperature, the permeability can be enhanced or reduced. We demonstrate that anesthetics decrease channel conductance and ultimately lead to 'blocking' of the lipid pores in experiments performed at or above the chain melting transition. Our data suggest that the macroscopic increase in permeability close to transitions and microscopic lipid channel formation are the same physical process.Comment: 12 pages, 6 figure

Recordings of the DMPC∶DLPC = 10∶1 membrane from Fig. 2 as a function of voltage (cf. Fig. 2, panel C4).

<p>Bottom: Current-traces for a DMPC∶DLPC = 10∶1 mol/mol membrane (150 mM KCl, T = 30°C) at four voltages showing an increase of single-channel conductance with voltage and an increased likelihood of channel formation. Top: The corresponding linear single-channel current-voltage relation indicating a single-channel conductance of  = 320 pS.</p