Ionic distributions and volume maintenance in human lymphocytes.

The equilibrium water contents and distributions of Na, K, Cl, Mg, Ca, and inorganic phosphate were studied under a variety of conditions that included 0 degrees C., low external K, ouabain and ATP-depletion. Net exclusion of Na was fully inhibited as manifested by a gain of cellular Na to a level greater than or equal to that in the environment. In none of these conditions did the cells swell in a manner expected in the classical pump-leak, double-Donnan concept of volume maintenance. Moreover, Na, K, Cl, and Mg fail to follow consistently a Donnan equilibrium in cells no longer able to exclude ions. Postulated volume-regulating mechanisms other than outwardly directed Na pumps, such as hydrostatic pressure, a Cl pump, altered charge or osmotic coefficient of proteins, and shrunken and swollen compartments did not explain the results. Therefore, we evaluated the data from the standpoint of a theory of cellular physiology in which cellular ions are adsorbed onto macromolecules. From these concepts and the data presented, a new theory of the maintenance and regulation of cellular volume, in which macromolecular salt-linkages provide a cohesive force, is discussed.