[The extracellular ionic environment and bone metabolism. In vitro study of the role of chloride]

Controversies surround the view that the blood-bone ionic equilibrium is controlled by ionic changes at a so called "bone membrane" that display a pump-leak mechanism able to maintain a concentration gradient for chloride in addition to that for calcium, sodium and potassium. On the other hand it is known that a chloride-bicarbonate transport is active at bone cells membrane to control cytosolic pH. We tested the hypothesis that a modification of the chloride concentration of the culture medium, as well as a block of the chloride-bicarbonate transport by an anionic channels blocker, in an experimental model that keeps intact the bone membrane, may influence the bone cells activity and that the influence may be quantitatively different to that previously observed in isolated bone cells. The experimental model is the intact fetal rat limb bone, cultured for 24 hours in a simplified medium at different chloride concentrations obtained by substituting chloride with isethionate. Alkaline phosphatase activity released in the medium was measured as a marker of osteoblasts activity. By progressively reducing the chloride concentration from 117 mM to 29 mM, alkaline phosphatase activity was found unchanged. By dramatically reducing the medium chloride concentration to the range 14-0 mM, alkaline phosphatase activity was significantly (p = 0.0002) inhibited by 31.58%.(ABSTRACT TRUNCATED AT 250 WORDS)