The mechanism by which pancreatic ducts secrete high HCO3- has not been fully resolved. This alkaline secretion can be achieved by transporting HCO3- from serosa to mucosa or by moving H+ in the opposite direction. Earlier studies have been focusing on HCO3- transport. In the accepted secretion model, basolateral Na+/H+ exchangers (NHE) and/or Na+-HCO3- cotransporters (NBC) contribute to cellular HCO3- accumulation, while luminal Cl-/HCO3- anion exchangers (AE) release HCO3- to lumen. Recently, we have considered the active H+ transporters, i.e. H+/K+ ATPases, and found them expressed and functional in rat pancreatic ducts (1). The aim of the present study was to determine whether also human pancreatic ducts express functional H+/K+ ATPases. The expression of H+/K+ ATPases was analyzed in human pancreatic duct cell lines (CAPAN-1, CFPAC-1 and PANC-1) by RT-PCR, western blot and immunostaining. Function of H+/K+ ATPases was estimated by intracellular pH (pHi) measurements in CAPAN-1 cells. Values are given as mean ± S.E.M., compared by paired student t-test. Both gastric and non-gastric alpha subunits of H+/K+ ATPases were found in CAPAN-1, CFPAC-1 and PANC-1 cells on both mRNA and protein levels (n=3 in each series). Also gastric beta-subunit of the pump was detected in duct cell lines (n=3). Localization of H+/K+ ATPase subunits in CAPAN-1 monolayers was confirmed by immunohistochemistry and confocal microscopy (n>10 preparations). In order to verify the function of pumps, we used Na+ and HCO3- free solutions to eliminate the contribution of NHE, NBC and AE on pHi. In ducts stimulated with secretin (1 nM), Na+ independent pHi recovery from acidosis was reduced by 75% in the presence of gastric H+/K+ ATPase inhibitor omeprazole (10 μM, n=6, p < 0.05); SCH28080 inhibited the recovery by 52% (10 μM, n=5, p < 0.05). We demonstrated both types of H+/K+ ATPases in human pancreatic duct cell lines, and their sensitivity to H+/K+ ATPase inhibitors indicates their potential role in the acid-base transport in human pancreas. We propose that the evidence for expression of H+/K+ ATPases in pancreas calls for revision of the model for HCO3-/H+ transport as well as for the use of proton pump inhibitors.