PfFit (ver2.01) is a three-part program for the calculation of osmotic water permeability of cell membrane (Pf) from volume changes of a spherical, wall-less cell, evoked by a non-instantaneous change of osmolarity in the external medium. The Pf calculation takes into account the rate of the osmolarity change.
It is a stand-alone MATLAB program written by Nava Moran and Menachem Moshelion, with GUI written by Roy Novik, compiled with the help of Deborah Weisman.
The basic assumptions and definitions underlying the algorithm of volume fitting are explained by Moshelion et al., 2004, including the Supplemental Material on the web (Dynamic Changes in the Osmotic water Permeability of Protoplast Plasma Membrane, by Menachem Moshelion, Nava Moran and Francois Chaumont, Plant Physiol., 135:2301-2317, doi: http://dx.doi.org/10.1104/pp.104.043000).
How to use PfFit in the context of an experiment is explained by Shatil-Cohen et al. , 2014 (Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example, by by Arava Shatil-Cohen, Hadas Sibony, Xavier Draye, François Chaumont, Nava Moran and Menachem Moshelion, JoVE, the Journal of Visualized Experiments, http://www.jove.com/video/51652) and further, in The PfFit User Guide (ibid.).
The PfFit program involves curve fitting. The ease of obtaining results may be deceptive!
Check the reported error values, strive for making it as small as possible, re-try the fit with many various sets of initial guesses!!! Create simulated data, add "noise", then try to fit - to get the feeling. Even a small improvement in error may be important!
Be cautious and skeptical!!
PfFit has three parts:
A: IndicatorFit, for determining the parameters of the time course of concentration changes of the bath osmoticum;
B: ModelMake, for generating simulations of bath osmoticum changes, changes of the osmotic water permeability (Pf) and of the cell volume changes;
C: VolumeFit, for extracting the osmotic water permeability (Pf) from the time course of changes in cell volume and the changes of bath osmoticum.
PfFit installer: http://www.jove.com/video/51652/