The Permeability of Normal and Malignant Cells to Water

Direct investigation of cell permeability has been necessarily limited in its material, since most of the cells of multicellular organisms have not been available for even roughly quantitative study during their life. Hence it is that most of our knowledge of the permeability of cell surfaces has been derived from experiments with plant cells, the eggs of certain invertebrates, and erythrocytes. It will readily be realized that it would be dangerous to form generalizations as to the permeability or osmotic properties of tissue cells on the basis of studies of other scattered types of cells. Even the red blood cells of various groups of vertebrates show striking divergences in their permeability both to water and to solutes (1). Considering the permeability of cells to simple substances as one of the fundamental phenomena of life, and in view of its importance in determining the accessibility of material to cells for metabolism and growth, an attempt has been made to determine quantitatively, as accurately as conditions permit, the permeability of tissue cells to water. In the preceding paper (2), we have described a method by which the surface and volume of certain fibroblasts can be estimated, and in the present study we have followed the change in cell volume while cells are subjected to a decreasing salt concentration in the surrounding medium. As we showed in the previous paper, it is impracticable to obtain cells which are susceptible of exact measurement except in a medium of clotted plasma. In this medium a number of radially symmetrical spindle-shaped or unduloidal cells can be found and measured. In experiments dealing with discrete cells such as the Arbacia egg or the erythrocyte, it is possible to make the practical assumption that the cell, as soon as placed in the anisotonic fluid medium, is surrounded by this medium so that its behavior is that of a cell placed suddenly in a given constant environment. Our material, on the other hand, is necessarily embedded in plasma at a greater or less distance from the experimental anisotonic medium; the environment of the cell is undergoing constant change and tends to reach equilibrium with the new medium more and more slowly as time goes on, as a function of the osmotic pressure gradient in the environs of the cell. If we consider that the diffusion coefficient and the temperature remain constant, then the rate of diffusion across a plane sheet is proportional to the concentration gradient between two infinitesimally separated points in the line of diffusion, according to Fick's law of diffusion. This is expressed mathematically as the second derivative formula: