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Eur Biophys J. 2018 Jul;47(5):499-514. doi: 10.1007/s00249-017-1268-9. Epub 2017 Nov 21.

Cell membrane biophysics with optical tweezers.

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LPO-COPEA, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, 21941-902, Brazil.
Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, 21941-972, Brazil.


Membrane elastic properties play important roles in regulating cell shape, motility, division and differentiation. Here I review optical tweezer (OT) investigations of membrane surface tension and bending modulus, emphasizing didactic aspects and insights provided for cell biology. OT measurements employ membrane-attached microspheres to extract long cylindrical nanotubes named tethers. The Helfrich-Canham theory yields elastic parameters in terms of tether radius and equilibrium extraction force. It assumes initial point-like microsphere attachment and no cytoskeleton content within tethers. Experimental force-displacement curves reveal violations of those assumptions, and I discuss proposed explanations of such discrepancies, as well as recommended OT protocols. Measurements of elastic parameters for predominant cell types in the central nervous system yield correlations between their values and cell function. Micro-rheology OT experiments extend these correlations to viscoelastic parameters. The results agree with a quasi-universal phenomenological scaling law and are interpreted in terms of the soft glass rheology model. Spontaneously-generated cell nanotube protrusions are also briefly reviewed, emphasizing common features with tethers. Filopodia as well as tunneling nanotubes (TNT), which connect distant cells and allow transfers between their cytoplasms, are discussed, including OT tether pulling from TNTs which mediate communication among bacteria, even of different species. Pathogens, including bacteria, viruses and prions, opportunistically exploit TNTs for cell-to-cell transmission of infection, indicating that TNTs have an ancient evolutionary origin.


Cell membrane nanotubes; Elastic properties; Optical tweezers

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