Influence of diffusion layers during osmotic flow across bimolecular lipid membranes

Abstract

It has been shown in previous papers that natural convection during osmotic flow is evidently an important consideration in the study of lipid bilayer permeability. If it does not occur, the osmotic permeability coefficient may well be considerably in error owing to boundary layer diffusion. Furthermore, the imposition of an osmotic flow on tritiated water diffusion produces a large increase in the rate of the latter process, presumably because the boundary layers are stirred by the natural convection. In the present paper the theory of natural convection in boundary layers is applied to osmosis across lipid bilayers and it is shown that, first, we should expect natural convection to minimize boundary layer errors in the osmotic permeability coefficient, but that even with natural convection some error may still be incurred by calculating the permeability directly from the bulk activities, and second, the rate of isotopic water exchange observed during osmotic flow is predicted by the theory.