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

TL;DR

This study reveals that lipid membrane permeability peaks near phase transitions, is quantized at the microscopic level, and is modulated by anesthetics, linking macroscopic permeability changes to lipid channel formation.

Contribution

It demonstrates the quantized nature of lipid pore conductance and connects permeability variations to heat capacity and anesthetic effects near phase transitions.

Findings

Permeability peaks near membrane melting transition.

Permeability is proportional to excess heat capacity.

Anesthetics modulate permeability and block lipid channels.

Abstract

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.