Proton-induced physicochemical calcium release from ceramic apatite disks.

When bone is cultured in acid medium there is net calcium efflux (JCa) and proton influx (JH) relative to the mineral. The acid medium appears to induce physicochemical mineral dissolution as well as cell-mediated bone resorption. To determine the independent effect of acid medium on physicochemical dissolution, we utilized cell-free synthetic ceramic apatite (CAP) disks, which contain carbonate (5.5%) in an apatite structure chemically similar to mammalian bone. CAP disks were cultured in control (Ctl, pH approximately equal to 7.44) or acid (Met, pH approximately equal to 7.11) medium for 48 h and compared to similarly treated neonatal (4-6 days old) mouse calvariae. Medium was changed and analyzed at 3, 24, and 48 h. At 3, 24, and 48 h there was significantly greater JCa from the CAP disks and calvariae incubated in Met compared to Ctl; over the entire 48 h time period there was a greater progressive increase in JCa from the CAP disks than the calvariae incubated in Met. There was no significant JCa at 3, 24, or 48 h from CAP disks or calvariae incubated in Ctl. At 3 h there was significantly greater JH into the CAP disks and calvariae incubated in Met compared to Ctl; JH was greater into the CAP disks than the calvariae. Utilizing a synthetic model of bone mineral we demonstrated that acid medium induces physicochemical calcium efflux and proton influx relative to the mineral.