Labeling by mepacrine and by LysoTracker are equally sensitive to deacidification in G1ME2-derived MKs. G1ME2-MKs were pretreated with vehicle alone (untreated) (A-B) or 100 nM bafA₁ (C) for 30 min and then labeled with 50 μM mepacrine (green) and 200 nM LysoTracker Red DND-99 for another 30 min in the presence of vehicle or bafA₁. Each of the images in panel A are deconvolved from raw, single-plane images shown in panel B; the images in panel C are raw. Corresponding DIC images are shown in panels A and C, and cell outlines based on DIC images are shown by the dotted line. Scale bars, 5 μm; ×2.5 magnifications of boxed region (insets). (D,E) Quantification of the standard deviation in signal intensity of labeling by mepacrine (D) and LysoTracker (E) in vehicle-treated cells (untreated; n = 30) or with bafA₁ (n = 30). The difference in signal intensity between treatments was evaluated by unpaired 2-tailed t test. G1ME2-MKs were imaged by spinning-disk confocal microscopy at room temperature with an Ultraview inverted microscope equipped with a 63× Plan Apochromat lens, a Hamamatsu Orca-ER CCD camera, and Volocity software. Imaging medium was IMDM. Mepacrine has an excitation/emission of 436/525 nm; LysoTracker Red excitation/emission: 577/590 nm. **P < .01. int., intensity.