DEVELOPMENT OF DRUG WHICH REGULATES BONE RESORPTION ACTIVITY IN OSTEOCLASTS VIA CYTOSKELTON AND SIGNAL TRANSDUCTION SYSTEM

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The aim of this study was to examine mechanisms of proton (H+ ) transport in active osteoclasts. We measured intracellular pH (pHi) changes in osteoclasts isolated on glasscoverslips or bone slices with a fluorescent pH indicator. H^+ was produced in osteoclasts by acid loading, and the pHi of the cells rapidly fell below the resting level. The decreased pHi did not recover in Na^+ free medium, but recovered in Na^+ rich medium. The pHi recovery was not observed on superfusion with Na+ rich medium containing amiloride, a potent sodium proton exchanger (NHE) inhibitor. The results reveal that osteoclasts on glass had H^+ transport system via NHE.In contrast, acid-loaded osteoclasts on bone showed their pHi recovery with amiloride and without Na+, presenting that active osteoclasts have H+ transport system other than NHE.From these results, osteoclasts have at least two different mechanisms of H+ transport compared to osteoclasts on glasscoverslips, suggesting that attachment to bone by osteoclasts activate intracellular signal transduction system.On the other hand, we evaluated the effects of bisphpsphonates on bone cells in rats fed with low calcium diet. Bone morphometrical analysis in femur and tibiae revealed that bisphpsphonates inhibited the increase of osteoclasts number, osteoclastic nucleus number, and osteoblasts number. Bisphpsphonates also inhibited the increment of mineralized nodule area and tartrate-resistant acid phosphatase positive-multi nuclear cells number. These results suggest that bisphpsphonates inhibit turnover in bone metabolism activated by low calcium diet.