Secretin dissipates red acridine orange fluorescence from pancreatic duct epithelium

This study was undertaken to elucidate whether duct cells in the pancreas contain acidic cytoplasmic compartments regulated by secretin. Microdissected pancreatic ducts from pigs were examined by acridine orange (AO) and 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein/tetraacetoxymethy l ester (BCECF/AM) epifluorescence microscopy. Estimated cytoplasmic pH using BCECF fluorescence was 7.43 +/- 0.04 and was not changed by altering CO2 tension in the incubation medium. The epithelium of acridine orange incubated peripheral interlobular pancreatic ducts exhibited green and red fluorescence; the colour depending on the experimental conditions. Red epithelial fluorescence was seen in resting pancreatic ducts and was greatly accentuated by raising CO2 in the incubation medium from 5.5 to 10 kPa. The red fluorescence was abolished by secretin, or following incubation with chloroquine or NH4Cl or the protonophores carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) or carbonyl cyanide m-chlorophenylhydrazone (CCCP), leaving uniform green fluorescence. These findings suggest that pancreatic duct cells contain CO2-dependent acidic compartments which vanish during secretin stimulation and which may be cytoplasmic tubulovesicles.