Effects of medium acidification by alteration of carbon dioxide or bicarbonate concentrations on the resorptive activity of rat osteoclasts.
Little is known about the extracellular conditions or factors that stimulate mature osteoclasts to resorb mineralized tissues. Isolated mammalian osteoclasts are strongly stimulated by protons in HEPES-buffered culture media in the absence of CO2 and HCO3-, but it has been reported that cell-mediated Ca2+ release from bone organ cultures is increased only when media are acidified by reduction of HCO3- concentrations, and not by increasing PCO2 (considered models of metabolic and respiratory acidosis, respectively). We investigated this question using disaggregated rat osteoclasts cultured on dentin slices for 24 h. The number of pits resorbed per osteoclast was stimulated in media acidified by manipulation of either HCO3- or CO2 concentrations. In experiments in which incubator CO2 was varied, resorption was almost abolished in the presence of 2.5% CO2 at pH 7.61 but increased in a stepwise manner up to 1.3 pits per osteoclast when dentin slices were cultured with 10% CO2 at pH 6.97. The depths and widths of pits, measured using a confocal laser reflection microscope, also tended to increase with increasing CO2 and decreasing pH. However, in experiments where pH was lowered by reducing medium HCO3-, pit size decreased, partially offsetting the increased number of pits resorbed per osteoclast. These findings suggest that rat osteoclasts may be more sensitive to stimulation by CO2 acidosis than by HCO3- acidosis, at least in the short term, and may possibly reflect local regulatory processes in bone.
Arnett
T R
TR
Department of Anatomy and Developmental Biology, University College London, England.
Boyde
A
A
Jones
S J
SJ
Taylor
M L
ML
D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000032:analysis; D001862:Bone Resorption; D002245:Carbon Dioxide / Q000032:analysis; D002478:Cells, Cultured; D003470:Culture Media; D006531:HEPES; D006863:Hydrogen-Ion Concentration; D010010:Osteoclasts / Q000166:cytology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D001639:Bicarbonates; D003470:Culture Media; D002245:Carbon Dioxide; D000135:Acid Phosphatase; D006531:HEPES