Cultured platelets increase in biomass and accumulate protein. (A) The bars represent the mean ± SEM for diameter (i), volume (ii), thickness (iii), and biomass (iv) of freshly isolated versus cultured platelets. *P < .05 versus baseline (i-iii) or 0 hours (iv). (B) The bars represent the mean ± SEM for total protein concentration of freshly isolated (Baseline) vs cultured platelets. *P < .05 versus baseline. (C) Left panels: Protein expression patterns for freshly isolated (Baseline) versus cultured (6 hours) platelets. These 2-dimensional gels, which are tilted in a third dimension to more effectively display the peak intensity and height of individual proteins, are representative of 5 independent experiments. (Right panel) The pie chart categorizes the protein expression patterns in freshly isolated versus cultured platelets. The categories are labeled as newly expressed (spots identified in cultured platelets that were not present at baseline), up-regulated (spots that were increased in cultured platelets compared with baseline), down-regulated (spots that were decreased in cultured platelets compared with baseline), or no change (spots that remained constant between cultured and baseline platelets). The percentages in the pie chart are the average of 5 independent experiments. (D) Platelets were coincubated with a fluorescent methionine analog (Met AA analog) in the presence or absence of puromycin. The top row identifies incorporation of methionine into newly synthesized protein. The bottom row panels (WGA) identify sialic acids. These panels are representative of 3 independent experiments.