| Research Abstract |
(1) To elucidate the electrophysiological properties of osteoblasts, we investigated the regulatory mechanism of chloride channel activity in a clonal osteoblastic cell line with the patch-clamp technique. In most of the insideout patches, the channel was activated only at a holding potential of around 0 mV,and was inactivated when the membrane potential was changed to a positive or a negative value. The voltage-dependency of channel activity was sensitive to intracellular Ca^<2+>. The single-channel conductance was about 340pS.The channel current was blocked by DIDS,reversibly at 10muM and irreversibly at 100muM.The channel was activated a few minutes after the excision of membrane patches in the absence of ATP.In presence of ATP (3mM), polymyxin B (20muM), an inhibitor of protein kinase C (PKC), activated the channel, but TPA (0.1muM) and OAG (1muM), potentactivators of PKC,inactivated the channel. Intracellular Ca^<2+> was not necessarily required for the channel activation, but it
… More
enhanced channel activity. The channel activation was found to be unaffected by okadaic acid (10muM), a specific inhibitor of types 1 and 2A phosphoprotein phosphatases.
These results suggest the following conclusion. In the presence of ATP,the channel protein or its related protein is phosphorylated by PKC,and the channel is inactivated and closes. In the absence of ATP,the protein is dephosphorylated probably by phosphoprotein phosphatases other than types 1 and 2A,and the channel is activated and opens. This reaction may be stimulated by Ca^<2+>.
(2) To investigate the relation of calcaneal bone atrophy to vertebral fracture and daily locomotion activity, we allied the ultrasound bone densitometry of the os calcis to osteoporotic patients in a rehabilitation hospital. In each subject, speed of sound (SOS) and broadband ultrasound attenuation (BUA) of the os calcis were measured with Achilles ultrasound bone densitometer (Lunar Corp.), and "Stiffness", an index of calcaneal bone atrophy, was defined from SOS and BUA.In this study, we examined the relation of Stiffness value to old compression fractures in vertebrae and daily locomotion activity. The mean Stiffness value of the osteoporotic patients was signeficantly lower than that of the normal control, and the mean value of the osteoporotic patients with old vertebral fracture was significantly lower than that without fracture. As for the daily locomotion activity, the value of the inpatients was significantly lower than that of the outpatients. The value of the patients with wheelchair activity was significantly lower than that with cane gait, and the value with cane gait was significantly lower than that with independent gait). There were statistically significant difference among the wheelchair activity, the cane gait, and the independent gait, respectively.
These suggest that ultrasound bone densitometry of the os calcis, which may fairly reflect the presence of old vertebral fracture and the state of daily locomotion activity, will be very useful both for risk-diagnosis of vertebral fracture and for rehabilitation program in osteoporosis. Less
|
