Recent developments in fluorescence lifetime imaging of lipid membrane dynamics

Lipid packing in cellular membranes exerts direct effect on membrane tension and microviscosity, and plays a central role in cellular adaptation, homeostasis and disease developement. According to conventional mechanical descriptions, viscosity and tension are directly interconnected, with increased tension leading to decreased membrane microviscosity. However, intricate molecular interactions that contribute to provide the structure and function of cellular membranes suggest a more complex relationship between these parameters. In this perspective, we review recent progress in using environmentally sensitive fluorophores to map changes in lipid structure, corresponding to alterations in the bilayer hydration, polarity, microviscosity or tension. We focus particularly on the use of Fluorescence Lifetime Imaging Microscopy (FLIM) that enables quantitative concentration-independent measurements of these parameters.