Studies of ions and water in human lymphocytes.

Abstract The conventional approach to the physiology of cellular ions, the membrane-osmotic-pump theory, is a paradigm that has guided the majority of workers in this field. In studies of human lymphocytes we found three sets of observations that are anomalous within the context of this theory and cannot be resolved by invoking any of the ad hoc mechanisms suggested to date. The anomalous observations include: (1) the maintenance of normal cellular volume when the ‘Na + pump’ is inhibited; (2) the inappropriately high rate of 22 Na efflux or of steady-state 22 Na exchange by cells that have gained Na + , and the dissociation of steady-state Na + exchange from steady-state K + exchange under a variety of conditions; and (3) the presence of a fast fraction of steady-state ion-exchange that is in series with the dominant slower exponential fraction, is intracellular in origin, and almost certainly reflects the actual permeability of the surface membrane. It was concluded that cellular surface-membrane processes are not the primary factors that control cellular ionic levels and cellular volume. Rather than attempt further to multiply hypotheses, we chose to evaluate a radically different concept of cellular physiology-the association-induction hypothesis. The association-induction hypothesis assumes: (1) much of cellular water exists in a physical state sufficiently ordered that it tends to exclude solutes and does so to varying degrees depending on the size and chemical properties of the solutes; this underlies the normal exclusion of Na + from the cell. (2) Cations may associate closely with fixed COO − groups on cell proteins that in the resting state of most cells prefer K + over Na + ; this underlies the normal accumulation of K + by the cell. (3) The unique properties of the polypeptide chain permit induced changes of electron distribution that allow site-to-site interaction in the association and dissociation of cations; this underlies the ability of the cell to change its selectivity from K + to Na + . Five sets of testable predictions and consequences are derived from these assumptions; (1) saturable and non-saturable fractions of cellular ions; (2) fast and slow fractions of isotopic ion-exchange that correspond, respectively, to the non-saturable and saturable components; (3) a cooperative interaction between ion-adsorbing sites; (4) a distinction between determinants of net ion-exchange (occupancy of adsorption sites undergoing changes in affinities for cations), and those of ionic self-exchange (activation energies for ion-site interaction under conditions of unchanging affinity of sites for cations); and (5) a requirement for fixed charge balance by association with ions. Results in the human lymphocyte were described that confirm these predictions and consequences, and that lead to reasonable explanations of the ‘anomalous’ data described above. All of the results obtained in lymphocytes are understood by reference to two general concepts: rapid solute exclusion from cellular water existing in an ordered state, and cation accumulation limited by adsorption onto and desorption from fixed anionic sites the majority of which interact with one another in a critical, cooperative, fashion. From these concepts, a new theory of the regulation of cellular volume is proposed. The major unsolved problems include an identification of the protein matrices that polarize cellular water, an identification of K + -adsorbing proteins in cells other than muscle, an understanding of ionic diffusion within the fixed-charged system, and a development of the concept of cell-volume regulation.