The Physiological Behavior of Rubidium and Cesium in Relation to That of Potassium

Interest in the biological properties of rubidium and cesium stems from their close physicochemical relationship to potassium. Reference to the Periodic Table shows these elements to be adjacent members of the Group I alkali metal series, which has the order: lithium, sodium, potassium, rubidium, cesium. In terms of their chemical behavior the elements of this series may be separated into two groups, the division falling between sodium and potassium. Potassium, rubidium, and cesium display very similar electrical, chemical, and physical properties, which differ only quantitatively in a well-defined manner. When considered in this context, a comparison of the biological behavior of these ions can provide much important information to the investigator concerned with the mechanisms handling the alkali metals in the living organism. A study of the comparative biochemistry of rubidium and cesium is therefore an excellent, although indirect, method for investigation of the normal biochemistry of potassium. The purpose of this paper is to review briefly certain aspects of the physiology of rubidium and cesium with particular reference to their relation to potassium. Space does not permit a complete or detailed discussion of this subject, and some active fields of investigation have been arbitrarily omitted. Emphasis has been chiefly placed on those topics most pertinent to mammalian, or at least vertebrate, physiology; newer developments in certain areas with which the author has had some personal experience have received greatest attention.