The determination of membrane transport parameters with the cell pressure probe: theory suggests that unstirred layers have significant impact

Abstract

ABSTRACTA simulation model was written to compute the time‐kinetics of turgor pressure, P, change in Chara corallina during cell pressure probe experiments. The model allowed for the contribution of a membrane plus zero, one, or two unstirred layers of any desired thickness. The hypothesis that a cell with an unstirred layer is a composite membrane that will follow the same kind of kinetics with or without unstirred layers was tested. Typical ‘osmotic pulse’ experiments yield biphasic curves with minimum or maximum pressures, Pmin(max), at time tmin(max) and a solute exponential decay with halftime . These observed data were then used to compute composite membrane properties, namely the parameters Lp = the hydraulic conductance, σ = reflection coefficient and Ps = solute permeability using theoretical equations. Using the simulation model, it was possible to fit an experimental data set to the same values of Pmin(max), tmin(max) and incorporating different, likely values of unstirred layer thickness, where each thickness requires a unique set of plasmalemma membrane values of Lp, σ and Ps. We conclude that it is not possible to compute plasmalemma membrane properties from cell pressure probe experiments without independent knowledge of the unstirred layer thickness.