Fickian Yet Non-Gaussian Nanoscopic Lipid Diffusion in the Raft-Mimetic Membrane.

Past experiments rationalized the observed dynamic heterogeneity and non-Gaussian diffusion in living cell membranes in terms of slow-active remodeling of the underlying cortical actin network. In this work, we demonstrate that the nanoscopic dynamic heterogeneity can also be explained via the lipid raft hypothesis, which postulates a phase separation between liquid-ordered (Lo) and liquid-disordered (Ld) nanodomains. Non-Gaussian displacement distribution is observed in the Lo domain for a long time, even when the mean square displacement becomes Fickian. This Fickian yet non-Gaussian diffusion is found particularly in the Lo/Ld interface consistent with the "diffusing diffusion" picture. A translational jump-diffusion model, previously employed to explain the diffusion-viscosity decoupling in supercooled water, is used here to quantitatively explain the long-term dynamic heterogeneity where a strong correlation between translational jump and non-Gaussian diffusion is observed. Therefore, this study proposes a novel approach to elucidate the dynamic heterogeneity and non-Gaussian diffusion in the cell membrane crucial for various cell membrane functionalities.