Figure 6.

The role of the P2Y₂ receptor in the inhibitory effects of ATP and UTP on bone mineralization. The inhibitory effects of (a) ATP and (b) UTP were 10-fold and 100-fold less potent, respectively, in P2Y₂R^−/− osteoblasts; mineralized bone nodule formation was 60% higher in P2Y₂R^−/− osteoblasts. The inhibitory actions of (c) ATP and (d) UTP on TNAP activity were lost in P2Y₂R^−/− osteoblasts. Basal TNAP activity was increased up to 40% in P2Y₂R^−/− cells. Values are mean ± SEM (n = 6), *p < 0.05, **p < 0.01, ***p < 0.001. Comparison of P2Y₂R^+/+ to P2Y₂R^−/−: ^#p < 0.05, ^##p < 0.01, ^###= p < 0.001. (E) Representative whole well scans (unstained) and phase contrast microscopy images (alizarin red stained) showing the effects of UTP on bone mineralization in P2Y₂R^−/− and P2Y₂R^+/+ osteoblasts. Areas of unmineralized matrix are highlighted by the arrows. Scale bars: whole well scans = 0.5 cm, microscopy images = 200 μm