On the role of Na,K-ATPase: a challenge for the membrane-pump and association-induction hypotheses.

The regulation of cellular ion levels has been an important issue of cell physiology since the beginning of the century. A special interest was focused on the monovalent ions which are involved in several cellular functions; in fact, the maintenance of high K+ level inside the cells is one of the most basic life-phenomena. Regarding the regulation of monovalent ions in general, two opposing ideas emerged: one being the membrane theory and the other the sorption theory(ies). Today most scientists are familiar only with the membrane theory which involves the pump and leak hypothesis and only a few consider the predictions of the association-induction hypothesis which may be classified as one of the sorption theories. In the regulation of monovalent ions the Na,K-ATPase is a key-molecule according to the membrane theory but not considered that important by the association-induction hypothesis. In this paper, we present two simple experiments which demonstrate the possible role of this molecule in the regulation of cellular Na+, K+ homeostasis and also disprove the pump and leak hypothesis.