The primary focus of this communication is to present an updated and advanced version of the theory of close-contact association of molecules and ions through the spatial fixation and aggregation of the adsorbing sites. The last sections of the text also review a collection of relevant in vitro and in vivo experimental findings gathering since seventy years ago. Though some of these findings were published before the theory, old and new, they all support the theory that close-contact association with the beta-, and gamma-carboxyl groups of intracellular proteins causes the selective accumulation of potassium ions (K+) in living cells.