Label-free and charge-sensitive dynamic imaging of lipid membrane hydration on millisecond time scales
| Autor: | Sylvie Roke, Orly B. Tarun, Christof Hannesschläger, Peter Pohl |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
0301 basic medicine
surface potential Time Factors Materials science Membrane lipids water Lipid Bilayers 010402 general chemistry 01 natural sciences Quantitative Biology::Cell Behavior Membrane Potentials Quantitative Biology::Subcellular Processes lipids Diffusion Membrane Lipids 03 medical and health sciences Lipid bilayer Membrane potential Physics::Biological Physics Millisecond Microscopy Confocal Multidisciplinary Membrane structure Biological membrane Biological Sciences 0104 chemical sciences Chemistry Biophysics and Computational Biology 030104 developmental biology Membrane membranes second-harmonic imaging Ionic strength Physical Sciences Biophysics Hydrophobic and Hydrophilic Interactions |
| Zdroj: | Proceedings of the National Academy of Sciences of the United States of America |
| ISSN: | 1091-6490 0027-8424 |
| Popis: | Significance Lipid bilayer membranes are responsible for compartmentalization, signaling, transport, and flow of charge in living cells. Membranes self-assemble in aqueous solutions. Without a hydrating environment, membranes cannot exist. It is therefore surprising to note that the hydrating water is neglected in most membrane-related studies. We imaged membrane-bound oriented water by means of label-free second harmonic microscopy. We tracked, on millisecond time scales, membrane domain diffusion of condensed charged lipid domains, domain structure, and the spatial distribution of charge. Real-time electrostatic membrane potential maps were constructed using nonlinear optical theory. The spatiotemporal fluctuation in the membrane potential is surprisingly large and reveals the importance of charge fluctuations on membranes. Biological membranes are highly dynamic and complex lipid bilayers, responsible for the fate of living cells. To achieve this function, the hydrating environment is crucial. However, membrane imaging typically neglects water, focusing on the insertion of probes, resonant responses of lipids, or the hydrophobic core. Owing to a recent improvement of second-harmonic (SH) imaging throughput by three orders of magnitude, we show here that we can use SH microscopy to follow membrane hydration of freestanding lipid bilayers on millisecond time scales. Instead of using the UV/VIS resonant response of specific membrane-inserted fluorophores to record static SH images over time scales of >1,000 s, we SH imaged symmetric and asymmetric lipid membranes, while varying the ionic strength and pH of the adjacent solutions. We show that the nonresonant SH response of water molecules aligned by charge−dipole interactions with charged lipids can be used as a label-free probe of membrane structure and dynamics. Lipid domain diffusion is imaged label-free by means of the hydration of charged domains. The orientational ordering of water is used to construct electrostatic membrane potential maps. The average membrane potential depends quadratically on an applied external bias, which is modeled by nonlinear optical theory. Spatiotemporal fluctuations on the order of 100-mV changes in the membrane potential are seen. These changes imply that membranes are very dynamic, not only in their structure but also in their membrane potential landscape. This may have important consequences for membrane function, mechanical stability, and protein/pore distributions. |
| Databáze: | OpenAIRE |
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