pH in the tPA-EGFP-containing granule. (Top panel) Distribution of pH in tPA-EGFP containing puncta, determined from measurements of individual tPA-EGFP puncta using the NH₄Cl pulse technique¹¹  6 hours after Nucleofection (mean pH; pH 6.10 ± 0.32, n = 89 organelles, 11 cells). (Bottom panel) Similar data obtained 24 hours after Nucleofection (mean pH; pH 6.11 ± 0.25, n = 52 organelles, 4 cells). The distribution of pH within individual mature WPBs containing tPA-EGFP is shown as a histogram with dashed lines (mean pH; pH 5.27 ± 0.23, n = 56 organelles, 10 cells). Intragranule pH was determined as described in “pH in the tPA organelle.”