The Exchange of Ions between Cells and Extracellular Fluid: The Uptake of Potassium into the Chorion Membrane from the Hen's Egg

Summary. The fact that living cells both in animals and plants are generally permeable both to kations and anions makes it necessary to investigate the mechanisms by which the large differences in concentration of single ions inside and outside cells are maintained. As a consequence of the general and free permeability for water the osmotic pressures inside and outside animal cells must be identical, and this involves the presence of at least a large fraction of the ions in the free state, because no other substances are available to reach such high concentrations. Methods are described to study the transfer of ions between cells and extracellular fluid in isolated chorion membranes from the hens egg, to prepare ultrafiltrates from these membranes and to distribute the ions determined on cells and extracellular solution. The chorion membranes are made up of two layers of epithelium and a loose network of primitive connective tissue cells with large extracellular spaces. Approximate measurements of numbers and dimensions of the separate cell types are presented. It is found that prolonged washing with potassium free Tyrode solution will reduce the K+ content of the cells to about half the normal (50 millimoles), the K+ being replaced by Na+, while K+ will be absorbed by the cells from the outside solution containing at the start 15 to 3 mM K+ down to concentrations of 1 millimole or less, raising the concentration of the ultrafiltrate from the cells above 100 millimoles. Simultaneously Na+ is removed from the cells against the outside concentration of about 150 mM. The two ions together with the undetermined anions make up a very large fraction of the total osmotic pressure of the solution in each cell. The active transfer of ions in both directions requires energy which appears to be provided mainly by non oxidative breakdown of carbohydrate and can go on at least for some time in the absence of free oxygen. At low temperature (3°–7°) the active transfer is reduced or abolished and the diffusion tends to equalize the concentration of each ion across the protoplasmic boundary film. It is pointed out in the discussion that specific structures and mechanisms involving a binding of the ions of elements in the boundary film must be assumed to account for the active transfer. The mosaic membrane model proposed by Lundegårdh is discussed and it is shown that the “points” responsible for potassium uptake are probably spaced at comparatively large distances apart. The possible mechanisms for regulating the transfer are briefly discussed.