Human ABCC4 is expressed at the plasma membrane. (A) Immunoblots of whole-platelet lysates loaded at the indicated concentrations, derived from healthy human donor and probed with ABCC4, ABCG2, ABCB1, ABCC1, and actin antibodies. (B) A representative immunoblot of biotinylated plasma membrane bound to streptavidin beads and the intracellular contents (SN) prepared from human platelets probed with human ABCC4, Na/K ATPase, and P-selectin antibodies. (C) After densitometry and normalization by total the amount in each fraction was expressed as a proportion of total. (D) The proportion of ABCC4, Na⁺/K⁺-ATPase, and P-selectin was quantified by densitometry and plotted as a bar graph. Each experiment was performed at least 3 times with the error bar representing one standard error of the mean. (D) Super resolution using structured illumination microscopy (SIM) to localize proteins stained with antibodies to human ABCC4 (green), Na⁺/K⁺-ATPase (blue), and actin (red). Two cross-sectional views (XZ and YZ) show plasma membrane localized ABCC4 (gray arrows). The dashed white line represents the junction where the platelet attaches to the coverslip, whereas the white line traces the outline of the platelet shape, and the yellow arrow represents the intracellular portion of the platelet defined by actin staining and devoid of ABCC4 staining. The scale bar corresponds to 1 μm for all 3 views.