PROTON-INDUCED PHYSICOCHEMICAL CALCIUM-RELEASE FROM CERAMIC APATITE DISKS

When bone is cultured in acid medium there is net calcium efflux (J(Ca )) and proton influx (J(H)) relative to the mineral. The acid medium a ppears to induce physicochemical mineral dissolution as well as cell-m ediated bone resorption. To determine the independent effect of acid m edium on physicochemical dissolution, we utilized cell-free synthetic ceramic apatite (CAP) disks, which contain carbonate (5.5%) in an apat ite structure chemically similar to mammalian bone. CAP disks were cul tured in control (Ctl, pH similar or equal to 7.44) or acid (Met, pH s imilar or equal to 7.11) medium for 48 h and compared to similarly tre ated neonatal (4-6 days old) mouse calvariae. Medium was changed and a nalyzed at 3, 24, and 48 h. At 3, 24, and 48 h there was significantly greater J(Ca) from the CAP disks and calvariae incubated in Met compa red to Ctl; over the entire 48 h time period there was a greater progr essive increase in J(Ca) from the CAP disks than the calvariae incubat ed in Met. There was no significant J(Ca) at 3, 24, or 48 h from CAP d isks or calvariae incubated in Ctl. At 3 h there was significantly gre ater J(H) into the CAP disks and calvariae incubated in Met compared t o Ctl; J(H) was greater into the CAP disks than the calvariae. Utilizi ng a synthetic model of bone mineral we demonstrated that acid medium induces physicochemical calcium efflux and proton influx relative to t he mineral.