Mechanism of Ca2+ regulation in osteoblast-like cells

초록

Physiological activity of osteoblast including bone formation is known to be closely related to the increase in intracellular Ca2+ activity of osteoblast. Ca2+ is an important intracellular messenger in diverse cellular functions, and the regulation of its level is mediated by the transmembrane Ca2+ movement via Ca2+ channels and Na+-Ca2+ exchange, and intracellular Ca2+ movement through the intracellular Ca2+ store. In the study, we investigated the mechanisms of intracellular Ca2+ regulation in osteoblast cells. Osteoblast-like cells (OLC) were isolated from femoral and tibia of neonatal rats, and cultured for 7 days. Cultured OLCs were loaded with Ca2+ -fluorescent dye Fura-2, and fluorescence images were monitored with a cooled CCD camera. High K+ (25mM) solution did not induce any significant [Ca2+]i increase. [Ca2+]i decreased when 0-Ca2+ solution was superfused, and returned to the basal level when the normal Tyrode solution (NT) was reperfused. However, when 1uM thapsigargin was applied with 0-Ca2+ superfusion solution, the reperfusion of NT elicited a transient increase of [Ca2+]i above the basal level, implying the existence of the store-dependent Ca2+ influx. When the extracellular [Na+] was replaced with N-methyl-D-glucosamine, an elevation of [Ca2+]i was observed. Occasionally, a spike-like transient [Ca2+]i increase was also observed. Occawionally, a spike-like transient [Ca2+]i increase was also observed, which was blocked by 1uM thapsigargin. The results from this study suggest that the intracellular Ca2+ activity in OLCs is regulated by transmembrane Ca2+ entry via Na+-Ca2+ exchange and intracellular Ca2+ stores.