Effect of cholesterol on permeability of carbon dioxide across lipid membranes

Abstract

Determining the permeability of lipid membranes to gases is important for understanding the biological mechanisms of gas transport. Experiments on model membranes have been used to determine the permeability of lipid bilayers in the absence of proteins. Previous measurements have used a number of different methods and obtained widely varying results. We have developed a microfluidic based microscopy assay that measures the rate of CO2 permeation in Giant Unilamellar Vesicles (GUVs), and we report permeability data for the POPC-cholesterol system. We find that cholesterol has a strong effect on permeability; bilayers containing high levels of cholesterol are an order of magnitude less permeable than bilayers without cholesterol, 9.9 {+/-} 1.0 x 10-4 cm/s vs. 9.6 {+/-} 1.4 x 10-3 cm/s. Statement of SignificanceDiffusion of dissolved gasses such as carbon dioxide through cell membranes is an important step in physiological processes. Key to understanding the behavior in cells is the measurement of gas diffusion through model lipid membranes, which isolates the effect of the lipids from other membrane components and allows for control of the composition. Previous measurements have yielded different results for the magnitude of gas transport, and have disagreed on the amount that cholesterol affects transport. The present study presents new data on gas transport across lipid mixtures containing cholesterol, and develops a microfluidic assay for gas transport that will enable further work.