EFFECTS OF CHANGING HYDROGEN-ION, CARBONIC-ACID, AND BICARBONATE CONCENTRATIONS ON BONE-RESORPTION INVITRO

We have examined the effects of H+, CO2, and HCO3 - concentrations during metabolic and respiratory acidosis and alkalosis on bone resorption in vitro. Rat fetal bones prelabeled with45CaCl2 were cultured at 2%, 5%, and 10% CO2 for up to 120 h, and the release of45Ca was measured in devitalized bones (non-cell-mediated45Ca release) and in live bones (cell-mediated45Ca release) cultured with or without PTH and 1,25(OH)2D3. Non-cell-mediated mineral loss was linearly related to H+ concentration but not to CO2 or HCO3 - concentration. This effect was observed on both labeled and stable calcium. Over a wide pH range (6.9-7.5) H+, CO2, or HCO3 - concentrations did not influence cell-mediated bone resorption in control or in PTH-and 1,25(OH)2D3-stimulated cultures. However, inhibition of cell-mediated bone resorption was observed at higher or lower pH irrespective of CO2 or HCO3 - concentrations. These observations demonstrate that the bone mineral mobilizing effect of acidosis in vitro is mainly due to the effect of changing H+ concentration on devitalized bone. Effects on cell-mediated bone resorption and hormonal response were observed only at extremes of pH. The effects of H+ were independent of changes in CO2 or HCO3 - concentration and could be responsible for the negative calcium balance and increased urinary loss observed in metabolic acidosis in vivo, but do not explain the reported differences in effects on calcium metabolism between respiratory and metabolic acidosis. © 1979 Springer-Verlag.