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Biophys. J. BioFAST: First Published November 11, 2005. doi:10.1529/biophysj.105.073809
© 2005 by the Biophysical Society.

A more recent version of this article appeared on February 1, 2006.
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BIOPHYSICAL THEORY AND MODELING

Simulations of (an)isotropic diffusion on curved biological surfaces

Ivo F Sbalzarini 1, Arnold Hayer 1, Ari Helenius 1 and Petros Koumoutsakos 1*

1 ETH Zurich

* To whom correspondence should be addressed. E-mail: petros{at}inf.ethz.ch.

Submitted on September 2, 2005
Revised on October 19, 2005
Accepted on 21 October 2005


  Abstract
We present a computational particle method for the simulation of isotropic and anisotropic diffusion on curved biological surfaces that have been reconstructed from image data. The method is capable of handling surfaces of high curvature and complex shape, that are often encountered in biology. The method is validated on simple benchmark problems and is shown to be second order accurate in space and time and of high parallel efficiency. It is applied to simulations of diffusion on the membrane of Endoplasmic Reticula (ER) in live cells. Diffusion simulations are conducted on geometries reconstructed from real ER samples and are compared to Fluorescence Recovery After Photobleaching (FRAP) experiments in the same ER samples using the transmembrane protein tsO45-VSV-G, C-terminally tagged with Green Fluorescent Protein (GFP). Such comparisons allow derivation of geometry-corrected molecular diffusion constants for membrane components from FRAP data. The results of the simulations indicate that the diffusion behavior of molecules in the ER membrane differs significantly from the volumetric diffusion of soluble molecules in the lumen of the same ER. The apparent speed of recovery differs by a factor of about 4, even when the molecular diffusion constants of the two molecules are identical. In addition, the specific shape of the membrane affects the recovery half-time, which if found to vary by a factor of about 2 in different ER samples.

Key Words: Diffusion, Endoplasmic Reticulum, FRAP, Simulations, curved surfaces, membranes




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Copyright © 2005 by the Biophysical Society.