Long and Short Lipid Molecules Experience the Same Interleaflet Drag in Lipid Bilayers

Membrane interleaflet viscosity ηₑ affects tether formation, phase separation into domains, cell shape changes, and budding. Contrary to the expected contribution to interleaflet coupling from interdigitation, the slide of lipid patches in opposing monolayers conferred the same value ηₑ≈3×10⁹ J s m^-4 for the friction experienced by the ends of both short and long chain fluorescent lipid analogues. Consistent with the weak dependence of the translational diffusion coefficient on lipid length, the in-layer viscosity was, albeit length dependent, much smaller than ηₑ.