Studies of diffusion in calvaria

Abstract

The rates of diffusion of small ions and neutral molecules through isolated calvaria have been determined. Compared with data published on self-diffusion and diffusion through cartilage, H₂O, 3-O-methylglucose, lactate, sulfate, and methylamine diffuse at approximately 2/3 the expected rate. Diffusion of H₂O and sulfate was unaffected by the administration of the diphosphonate 1-hydroxyethane-1,1-diphosphonate (EHDP), although phosphate fluxes are markedly diminished. Diffusion of water was nearly doubled by vitamin D deficiency. A 1-week treatment with 1,25(OH)₂D₃ had no effect on H₂O diffusion while returning calcium influx to normal. It is concluded that bone matrix permits a flow of small neutral and ionized molecules nearly comparable to that in cartilage. When changes in calcium and phosphate influx are observed, they can be ascribed to the exchange properties of bone mineral and not to changes in matrix permeability.