The Relationship of Sodium and Potassium to Carbonate in Bone* by William Ii. Bergstrom with the Technical Assistance of Ellen

Approximately a third of the total body sodium content of man, dogs, and rats is present in the inorganic portion of the skeleton (l-3). Although the magnitude of this fraction and its variability in acidosis and sodium depletion have been defined by direct analysis and by the use of isotopes, the precise position which sodium occupies in bone salt remains obscure. Harrison (4), pointing out the association of sodium with the carbonate of naturally occurring apatites, suggested that it might be present as carbonate. Neuman et al. (5), studying fluoride uptake by bone salt in vitro, concluded that their data could best be interpreted by assuming that some of the carbonate present shared a monovalent bond with calcium, and that the second carbonate valence was occupied by sodium, i.e. Ca-0-CO-Na. In at least two instances substantial changes occur in the sodium and carbonate content of bone, namely, during growth and in acidosis. It has long been known that bone carbonate shows a gradual but significant increase with maturation (6), and increments of bone sodium with age have been more recently demonstrated (7). Irving and Chute (8) found decreased bone carbonate in rats undergoing oral HCI loads; acute and chronic sodium deprivation and acidosis have resulted in significant decrements of bone sodium. It therefore appeared desirable to measure both sodium and carbonate simultaneously in normal bone of varying age and in the bone of acidotic animals in order to determine whether the changes observed might suggest a relationship helpful in determining the position of bone sodium. Since previous work (7) has shown that bone also contains significant amounts of potassium, this cation was included in the present study.