Agonist-induced surface expression of lysosomal membrane proteins is impaired in HPS model platelets. Washed platelets from WT, pallid, pearl, or light ear mice were stimulated as indicated with thrombin (A-D) or convulxin (E and F) for 10 minutes in the absence or presence of 10 μM ADP and then analyzed by flow cytometry for surface LAMP1 or LAMP2. Shown is the percentage of cells with labeling above the background observed on unstimulated cells (see supplemental Figure 4A,B for gating strategy and examples of flow cytometry profiles). Data represent mean ± standard deviation from at least 3 independent experiments. *P < .05; **P < .01; ***P < .005 for HPS models vs WT.