Simultaneous net accumulation of both K+ and Na+ by lymphocytes at 0 degrees C.

Human lymphocytes at 0 degrees C in low Na+ medium accumulate both K+ and Na+ to levels higher than in the external medium. This is not due to an impermeable compartment or a Donnan equilibrium, and is incompatible with the membrane Na+-pump concept. In contrast, it supports prior evidence that ion exchange in lymphocytes is mediated by adsorption onto and desorption from fixed anionic sites within the cell. Additional aspects of ion and water contents of cells in low Na+ medium are described and are explained by this concept.