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Biophys. J. BioFAST: First Published August 19, 2005. doi:10.1529/biophysj.105.063826
© 2005 by the Biophysical Society.

A more recent version of this article appeared on November 1, 2005.
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MEMBRANES

Indentation and adhesive probing of a cell membrane with AFM: model and experiments

Shamik Sen 1, Shyamsundar Subramanian 1 and Dennis Discher 1*

1 University of Pennsylvania

* To whom correspondence should be addressed. E-mail: discher{at}seas.upenn.edu.

Submitted on March 31, 2005
Revised on May 5, 2005
Accepted on 3 August 2005


  Abstract
In probing adhesion and cell mechanics by AFM, the mechanical properties of the membrane have an important if neglected role. Here we theoretically model the contact of an AFM tip with a cell membrane, where direct motivation and data are derived from a prototypical ligand-receptor adhesion experiment. An AFM tip is functionalized with the representative ligand SIRP{alpha} and then used to probe its native receptor on red cells, CD47. The interactions prove specific and typical in force, and also show in detachment, a sawtooth-shaped disruption process that can extend over 100's of nm. The theoretical model here that accounts for both membrane indentation as well as membrane extension in tip retraction incorporates membrane tension and elasticity as well as AFM tip geometry and stochastic disruption. Importantly, indentation depth proves initially proportional to membrane tension and does not follow the standard Hertz model. Computations of detachment confirm non-periodic disruption with membrane extensions of 100's of nm's set by membrane tension. Membrane mechanical properties thus clearly influence AFM probing of cells, including single molecule adhesion experiments.

Key Words: AFM, adhesion, erythrocyte, membrane, tension




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Copyright © 2005 by the Biophysical Society.