Nanoscale Cell Membrane Fluctuations Measured by Scanning Ion Conductance Microscopy

Abstract

Nanoscale membrane fluctuations in epithelial cells connected to neighboring cells were quantified by scanning ion conductance microscopy (SICM), which is intrinsically a non-contact technique and widely used for imaging soft cell surfaces at high resolution. In this study, we first proposed a model for the estimation of apical cell membrane fluctuations from the ion current curves, i.e., the ion current vs. the tip-surface distance. Mapping the ion current curves with a commercial SICM apparatus (XE-Bio, Park Systems, Korea) revealed that, in untreated Madin-Darby canine kidney (MDCK) epithelial cells in a confluent condition, the fluctuation amplitude of apical membranes increased towards the cell center. Moreover, it was found that the spatial dependence disappeared when actin filaments were disrupted, which caused a significant enhancement of cell membrane fluctuations. The measurements of the complex shear modulus of cells by atomic force microscopy (AFM) suggested that the mechanical properties of the cells are not directly correlated with cell membrane fluctuations. The results indicate that membrane fluctuations are highly constrained at the cell-cell interface, in the vertical direction to the apical cell surface and by the underlying actin filaments.