The effects of temperature and ouabain on steady‐state Na and K exchanges in human lymphocytes

The temperature‐dependence of steady‐state exchanges of K and Na were determined under conditions in which cell viability, ATP, water, Ca, and Mg were not confounding variables. Steady‐state ion contents are near‐normal between 37° and 10° C, Below 10° C K is replaced by Na in a mole‐for‐mole fashion with significant net K retention and Na exclusion occurring even below 3°C. The rates of steady‐state Kand Na exchanges have markedly different temperature‐dependences; between 37° and 10° C, for example, that of K decreases markedly while that of Na remains near‐normal, and there is no consistent correlation between the steady‐state exchanges and the ionic contents. Ouabain increases steady‐state Na flux at 37° C and induces a more marked temperature‐dependence over the entire temperature range. This effect is not due simply to inhibition of some processes and unmasking others; it mirrors a pronounced effect of ouabain on the intrinsic properties of Na self‐exchange. These results are compatible with a model based on two simple concepts: (1) partial ionic exclusion from cellular water that is ordered by interaction with proteins; and (2) ionic accumulation mediated by adsorption onto and desorption from fixed macromolecular anionic sites, the majority of which interact with one another in a cooperative fashion. In this view, the sharp temperature transition in the net replacement of K by Na below 10° C is due to a critical transition in the selectivity of the cooperatively interacting adsorption sites. The rates of steady‐state self‐exchanges of K and Na are determined by parameters of ion‐site interaction, and the major set of ion‐adsorbing sites that interact cooperatively have a steep thermal activation energy of ionic self‐exchange. When they are in the K‐preferring state above 10° C, exchange of K has a steep temperature‐dependence. When they are in the Na‐preferring state below 10° C, exchange of Na has a steep temperature‐dependence. When these sites are forced into a Na‐preferring state at all temperatures by treatment with ouabain, exchange of Na acquires a steep temperature‐dependence over the entire temperature range 37° to 0° C.