Acid secretion by parietal cells. LysoSensor™ Yellow/Blue DND-160 was used to monitor the acid secretion by live parietal cells incubated either by Cim or His/IBMX. Cell Tracker Red CMTPX was used to track all live cells. Some apical vacuoles of parietal cells in resting stage revealed several small areas with weak yellow fluorescence, indicating basal acid secretion (A). Parietal cell treated with His/IBMX showed an expansion of apical vacuoles, as shown by strongly enlarged zones with yellow fluorescence, indicating the continuous secretion of acid (B). Cim: Cimitidine; His: histamine; IBMX: 3-isobutyl-1-methylxanthine.