Single-cell force spectroscopy membrane stretches (nanotubes) can be pulled out from cells, even for many micrometers. Does the rupture force depend on their length or diameter? Does their diameter change upon pulling?
A diploma student of me accidently discovered such nanotubes on supported lipid bilayers. They are also formed in force-spectroscopy experiments on pore-spanning membranes (10.1002/smll.201101557). The tether force was independent of the tether length (force plateau) showed a "most probable" lifetime. In 2009 Daniel J Müller and coworkers published a nice review (10.1038/nchembio.181): The tether force is a measure of isotropic tension, bending rigidity and extension velocity (in combination with viscosity) of the cell membrane. Consequently you are right that the force depends on the diameter and when the properties of your membranes are known, you may calculate it (10.1038/nrm1784).
The non-exponential decay of tether lifetimes indicates, that they to not simply detach from the cantilever/tweezers bead, but somehow collapse. This assumption is supported by recent theoretical calculations (10.1016/j.bpj.2012.03.048).
Can we calculate tether diameter using AFM or do we need optical tweezers ???
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