Potassium effects on bone: comparison of two model systems.

Effects of elevated potassium on bone resorption and on the inhibition by ouabain of parathyroid hormone (PTH)-stimulated resorption were studied in neonatal mouse calvaria, fetal mouse limb bones, and fetal rat limb bones. Ouabain inhibited PTH-stimulated resorption, and K at least partially reversed the inhibition by ouabain in all three systems. However, in contrast to calvaria, neither limb bone system was stimulated to resorb by increased K. Although the reversal of ouabain inhibition in all three systems was likely mediated by an effect on Na-K-ATPase, the resorptive effect of K alone must occur by a different mechanism because it was seen only in the calvaria. The production of prostaglandins may play a partial role in the mechanism of the stimulation of Ca release from calvaria by K. Potassium (35 mM) stimulated production of PGE2 by calvaria but not by limb bones. Indomethacin inhibited the increase in PGE2 in calvaria and partially blocked the stimulated bone resorption observed in response to K. The fetal rat limb bone cultures also differed from the mouse calvaria in being more readily inhibited by increased osmolarity. Thus, secondary effects may be responsible for the variant responses of different bone tissues to certain stimuli.