EVIDENCE FOR A NA-CA2+ EXCHANGER IN RAT PANCREATIC DUCTS()

Only recently has it been recognized that intracellular Ca2+ is an imp ortant cellular mediator in pancreatic ducts. The aim of the present s tudy was to characterize the Ca2+ efflux pathway in ducts freshly prep ared from rat pancreas, Lowering of extracellular Na+ concentration re sulted in a significant increase in intracellular Ca2+. This effect wa s fast, reversible, dependent on the extracellular Na+ concentration a cid did not correlate with intracellular pH changes. It was abolished in Ca2+-free solutions, indicating that the outwardly directed Na+ gra dient was directly coupled to a flufenamate insensitive Ca2+ influx, R emoval and reintroduction of extracellular Na+ induced transient hyper polarization and depolarization of V-m, respectively, Taken together, our data indicate that pancreatic ducts possess an electrogenic Na+-Ca 2+ exchanger, which under control conditions is responsible for transp orting Ca2+ out of resting duct cells.