Figure 4. Effects of LPA on alkaline phosphatase activity and expression of differentiation markers. (A) DPF were stimulated for 72 hrs with bone morphogenetic protein-7 (BMP-7) as indicated under serum-free conditions and stained for alkaline phosphatase activity where positive cells appear blue (AP⁺). (B) Amount of alkaline phosphatase activity per microscopic field, normalized to unstimulated controls. Data are given as means and standard deviation from results of two random selected preparations, each performed in triplicate. *P < 0.05 vs. unstimulated control; **P < 0.01 between marked groups. (C) Representative picture of a microscopic field that shows alkaline-phosphatase-positive cells given in blue. (D) RT-PCR analysis of mRNA isolated from DPF incubated with LPA for 72 hrs.