Bicarbonate Transport by the Human Pancreatic Ductal Cell Line HPAF

Objectives: The human pancreatic duct cell line, HPAF, has been shown previously to secrete Cl-in response to Ca2+-mobilizing stimuli. Our aim was to assess the capacity of HPAF cells to transport and secrete HCO3-. Methods: HPAF cells were grown as confluent monolayers on permeable supports. Short-circuit current was measured by voltage clamp. Intracellular pH (pH(i)) was measured by microfluorometry in cells loaded with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Results: In HCO3--free solutions, ATP-evoked changes in short-circuit current were inhibited by bumetanide, and the recovery of pHi from acid loading was abolished by 5-(N-ethyl-N-isopropyl)-amiloride (EIPA). In the presence of HCO3, ATP-evoked secretion was no longer inhibited by bumetanide, and there was a strong EIPA- insensitive recovery from acid loading, which was inhibited by 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonate (H2DIDS). ATP, but not forskolin, stimulated HCO3- efflux from the cells. Conclusions: In the absence of HCO3-, ATP-evoked Cl- secretion is driven by a basolateral Na+-K+-2Cl(-) cotransporter, and pH(i) is regulated by apical and basolateral Na+/H+ exchangers. In the presence of HCO3-, ATP-evoked secretion is sustained in the absence of Na+-K+-2Cl(-) cotransporter activity and is probably driven by basolateral Na+-HCO3- cotransport.