Effect of hydrostatic pressure on the percentage of TRAP positive cells. MP (5 × 105/ml) from healthy volunteers were cultured at 5 × 105 cells/ml on Thermanox coverslips in supplemented medium for 7 days before pressurisation (34.5 × 10-3MPa) (5.0 psi) for four cycles of pressure. MP were fixed and stained for TRAP. For each sample, the number of positive and negative cells in 5 random microscope fields was counted, for each of three replicates. Results are the mean and SD of 5 separate experiments.