Hydrodynamic damping of membrane thermal fluctuations near surfaces imaged by fluorescence interference microscopy.

Hydrodynamic coupling between closely apposed lipid bilayer membranes can substantially slow the time scale of thermal fluctuations. These effects could dominate the kinetics of macromolecular interactions at membrane interfaces, and may exert important influences over the interactions between living cells. Here, we study a reconstituted membrane system consisting of two planar bilayers with average separation distances of 30-60 nm. This spacing range is comparable to that of natural intercellular junctions. Using real-time fluorescence interference contrast imaging, spatial and temporal characteristics of the thermal fluctuation spectra are monitored simultaneously. Strong hydrodynamic damping of the fluctuation time scale is observed whereas fluctuation spatial dimensions are unaltered by proximity to another surface. These observations provide experimental confirmation of recent theoretical models.