Broad lipid phase transitions in mammalian cell membranes measured by Laurdan fluorescence spectroscopy

Christoph Westerhausen,Nicolas Färber

doi:10.1016/j.bbamem.2021.183794

Christoph Westerhausen, Nicolas Färber

Open Access

https://doi.org/10.1016/j.bbamem.2021.183794

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Journal: BBA - Biomembranes	Publication Date: Oct 7, 2021
Citations: 12	License type: elsevier-specific: oa user license

Affiliation: University of Augsburg

Abstract

Employing fluorescence spectroscopy and the membrane-embedded dye Laurdan we experimentally show that linear changes of cell membrane order in the physiological temperature regime are part of broad order-disorder-phase transitions which extend over a much broader temperature range. Even though these extreme temperatures are usually not object of live science research due to failure of cellular functions, our findings help to understand and predict cell membrane properties under physiological conditions as they explain the underlying physics of a broad order-disorder phase transition. Therefore, we analyzed the membranes of various cell lines, red blood cell ghosts and lipid vesicles by spectral decomposition in a custom-made setup in a temperature range from −40 °C to +90 °C. While the generalized polarization as a measure for membrane order of artificial lipid membranes like phosphatidylcholine show sharp transitions as known from calorimetry measurements, living cells in a physiological temperature range do only show linear changes. However, extending the temperature range shows the existence of broad transitions and their sensitivity to cholesterol content, pH and anaesthetic. Moreover, adaptation to culture conditions like decreased temperature and morphological changes like detachment of adherent cells or dendrite growth are accompanied by changes in membrane order as well. The observed changes of the generalized polarization are equivalent to temperature changes dT in the range of +12 K < dT < -6 K.

Highlights

Synthetic lipid double layers exhibit cooperative phase transitions causing their physical properties such as heat capacity, volume, area, thickness, stiffness, compressibility, adhesion forces, permeability and diffusion coefficient to depend on temperature, pressure, pH, electric field, salt concentration etc. in a non-linear way [1,2,3,4,5,6,7,8,9]
This correlation of phase state typically measured by differential scanning calorimetry (DSC) and membrane properties is well investigated for artificially created lipid membranes such as supported lipid bilayers and vesicles
Our data proves that we are in case of 13:0PC, 14:0PC, 15:0PC and 15:0PC with 10% cholesterol able to detect the correct location of phase transitions in lipid membranes and peak width and height show similar behavior in both data sets

Summary

Introduction

Synthetic lipid double layers exhibit cooperative phase transitions causing their physical properties such as heat capacity, volume, area, thickness, stiffness, compressibility, adhesion forces, permeability and diffusion coefficient to depend on temperature, pressure, pH, electric field, salt concentration etc. in a non-linear way [1,2,3,4,5,6,7,8,9]. In a non-linear way [1,2,3,4,5,6,7,8,9] This correlation of phase state typically measured by differential scanning calorimetry (DSC) and membrane properties is well investigated for artificially created lipid membranes such as supported lipid bilayers and vesicles. If this concept holds for biological cell membranes it is possible to predict their response to environmental changes but manipulating membrane functions such as permeability becomes possible by changing physical parameters like temperature or pH. To determine the respective intensities we fit the spectral data by two lognormal functions as proposed by Bacalum et al [14]

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Conclusion