Inhibition of osteoclast formation and function by bicarbonate: role of soluble adenylyl cyclase

J Cell Physiol. 2009 Aug;220(2):332-40. doi: 10.1002/jcp.21767.


High [HCO(3)(-)] inhibits and low [HCO(3)(-)] stimulates bone resorption, which mediates part of the effect of chronic acidosis or acid feeding on bone. Soluble adenylyl cyclase (sAC) is a bicarbonate sensor that can potentially mediate the effect of bicarbonate on osteoclasts. Osteoclasts were incubated in 0, 12, and 24 mM HCO(3)(-) at pH 7.4 for 7-8 days and assayed for tartrate-resistant acid phosphatase (TRAP) and vacuolar-ATPase expression, and H+ accumulation. Total number and area of TRAP (+) multinucleated osteoclasts was decreased by HCO(3)(-) in a dose-dependent manner. V-ATPase expression and H+ accumulation normalized to cell cross-sectional area or protein were not significantly changed. The HCO(3)(-) -induced inhibition of osteoclast growth and differentiation was blocked by either 2-hydroxyestradiol, an inhibitor of sAC or sAC knockdown by sAC specific siRNA. The model of HCO(3)(-) inhibiting osteoclast via sAC was further supported by the fact that the HCO(3)(-) dose-response on osteoclasts is flat when cells were saturated with 8-bromo-cAMP, a permeant cAMP analog downstream from sAC thus simulating sAC activation. To confirm our in vitro findings in intact bone, we developed a 1-week mouse calvaria culture system where osteoclasts were shown to be viable. Bone volume density (BV/TV) determined by micro-computed tomography (microCT), was higher in 24 mM HCO(3)(-) compared to 12 mM HCO(3)(-) treated calvaria. This HCO(3)(-) effect on BV/TV was blocked by 2-hydroxyestradiol. In summary, sAC mediates the inhibition of osteoclast function by HCO(3)(-), by acting as a HCO(3)(-) sensor.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 8-Bromo Cyclic Adenosine Monophosphate / metabolism
  • Acid Phosphatase / metabolism
  • Adenylyl Cyclases / pharmacology*
  • Animals
  • Bicarbonates / pharmacology*
  • Cell Differentiation / drug effects
  • Cell Differentiation / physiology
  • Cell Line
  • Cells, Cultured
  • Estradiol / analogs & derivatives
  • Estradiol / pharmacology
  • Female
  • Humans
  • Isoenzymes / metabolism
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Osteoclasts / cytology
  • Osteoclasts / drug effects*
  • Osteoclasts / physiology*
  • Protons
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Skull / cytology
  • Skull / drug effects
  • Skull / metabolism
  • Tartrate-Resistant Acid Phosphatase
  • Vacuolar Proton-Translocating ATPases / metabolism


  • Bicarbonates
  • Isoenzymes
  • Protons
  • RNA, Small Interfering
  • 8-Bromo Cyclic Adenosine Monophosphate
  • Estradiol
  • 2-hydroxyestradiol
  • Acid Phosphatase
  • Acp5 protein, mouse
  • Tartrate-Resistant Acid Phosphatase
  • Vacuolar Proton-Translocating ATPases
  • Adenylyl Cyclases