Mechanoreceptors in Alveolar Osteocyte

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Although it is well known that bone formation is accelerated by mechanical stimuli, the signal transduction pathways involved are largely unknown. Suggested by the studies by E.Burger and others, which showed that bone cells respond to high-level and low-level stresses differently, we compared the response of newborn rat calvarial cells to mechanical stress during their development from immature osteoblasts to mature osteoblasts, further into osteocytes. We showed that the type of cells which is most sensitive to physiological stretching of less than 4,0000 mustrain is not osteoblast but young osteocyte. These cells are in transition from osteoblasts to osteocytes expressing low-level alkaline phosphatase and high-level osteocalcin. They also develop extensive cell processes which form a network of cells in bone. These young osteocytes stop proliferation in response to stretching and mineralize thir matrix. It was shown that cAMP is secreted and the expression of IGF-I and osteocalcin is induced in response to the stress.In human alveolar bone, it was not easy to clean the bone chips prior to the isolation of cells. That is probably why we could not obtain as many differentiated osteocytes as in rat calvaria. In those few successful cases, however, the response of osteocytes to the above mentioned stretching was similar to that of rat osteocytes. In other words, it was shown by RT-PCR method that osteocalcin expression was upregulated as a result of stretching. It was also suggested that amiloride sensitive channel (s) is involved in their response to stretching from our results of channel blocker studies measuringCa influx upon the exposure to lower osmotic conditions.