Effect of the PDE4 inhibitor EMD95833 on fibroblastic colony formation and osteoblastic differentiation. Whole bone marrow was prepared and cultured in the CFU-f assay as described in the text and treated with varying concentrations of EMD95833. In order to assess the effects of EMD95833 on osteoblastic differentiation, after fixation the cells were stained for alkaline phosphatase with naphtholphosphate/fast red, calcium deposition with alizarin red and total colonies with methylene blue. Data presented are mean colony numbers per Petri dish ± S.D. * Denotes significant difference from the appropriately stained control cultures, p < 0.05.