OKADAIC ACID INHIBITS ALKALINE-PHOSPHATASE ACTIVITY IN MC3T3-E1 CELLS

Alkaline phosphatase activity is regulated by various hormones and gro wth factors at least in part through the phosphorylation of target pro teins during the bone cell differentiation. To investigate the role of protein phosphorylation in alkaline phosphatase activity in MC3T3-E1 osteoblast, we used okadaic acid which is a potent specific inhibitor of serine/threonine protein phosphatases of type 1 and 2A. Alkaline ph osphatase activity in cellular layer was measured by spectrophotometer using p-nitrophenyl phosphate as substrate and data were expressed as p-nitrophenol of nmol/min/mg of protein. Okadaic acid (1-50 ng/ml) ca used the inhibition of alkaline phosphatase activity in MC3T3-E1 cells . At 50 ng/ml of okadaic acid showed the maximal inhibitory effect on alkaline phosphatase activity. Okadaic acid (50 ng/ml) also inhibited alkaline phosphatase activity in all differentiation stages. These res ults indicate that okadaic acid inhibits alkaline phosphatase activity in MC3T3-E1 cells.