Determination of volume and water permeability of plated cells from measurements of light scattering.

Measurements of cell membrane water osmotic permeabilities can be inaccurate because of the technical difficulties inherent to cell volume measurements and because of the presence of an unstirred water layer in contact with the cells. We detail here a method we have developed to quantify transient changes in cell volumes from the intensity of light scattered by cells. For this, we theorize how an unstirred layer originates in a perfusing chamber, and we calculate values for both cell membrane water osmotic permeability and unstirred layer thickness from time transient changes in scattered light. We apply a computer algorithm that finds the best correspondence between experimental data and estimated values. This is done by solving a differential equation governing cell volume changes by numerical integration (Runge-Kutta) and iterating the procedure varying the test values of osmotic permeability and unstirred layer thickness until the best fit is achieved. We exemplify this procedure with experimental results obtained in adherent cultured cells.