Figure 1.

Role of aquaporins in isotonic fluid secretion and zymogen granule exocytosis in the exocrine pancreas. The primary function of pancreatic acinar cells is to synthesize and secrete digestive enzymes, which are stored in zymogen granules in the apical poles. AQP12, which is located in the cytoplasm, contributes to the proper formation, maturation and exocytosis of zymogen granules, a process dependent on water transport across the membranes. Acinar cells also secrete a small volume of a NaCl-enriched isotonic fluid. The water efflux from acinar cells to the lumen is mainly mediated by AQP8. Ductal cells secrete Na⁺, Cl⁻, HCO3⁻ as well as large amounts of water via AQP1 and AQP5 in order to form the final isotonic pancreatic fluid.