Passive accumulation of magnesium, sodium, and potassium by chick calvaria

Four-day-old chick calvaria were used to determine the passive concentrations of magnesium, sodium, and potassium in metabolically poisoned bone. When incubated in buffers containing the blood levels of sodium and magnesium, these calvaria contained sodium and magnesium at the identical concentrations found in freshly dissected calvaria. Calvarial sodium and magnesium levels could be varied by altering the buffer concentrations of these cations. The potassium content of metabolically poisoned calvaria incubated in buffers containing 4 mM potassium was less than 20% of the content of freshly dissected calvaria. When the buffer concentrations of sodium and potassium were systematically varied, ouabain-poisoned calvaria concentrated these cations in the bone extracellular fluid by a factor of approximately two above buffer cation levels. Presumably, the hydroxyapatite crystal zeta potential is responsible for this concentrative phenomenon. These results are discussed in terms of the control of the ionic content of the bone extracellular fluid by the postulated "bone membrane."