Chloride-bicarbonate exchange in isolated rat pancreatic acini

We have measured the intracellular pH (pHi) of single isolated rat pancreatic acini using the fluorescent dye dicyano-hydroquinone (DCH). Steady-state pHi was unaffected by either acetylcholine (10 microM), caerulein (10 nM) or secretin (1 nM), or by the anion exchange inhibitor DIDS (1 mM) and only changed by 0.32 units when extracellular pH was varied over the range from 6.8 to 8.4. However, replacing extracellular chloride with gluconate, such that the final bath chloride concentration was less than 20 mM, caused a marked alkalinization of pHi to a new steady-state value. The rate of pHi alkalinization under these conditions was bicarbonate-dependent, blocked by pre-incubation of the acini with 1 mM-DIDS, but unaffected by removal of extracellular sodium. These observations are consistent with the presence of a Cl- -HCO3- exchanger on rat pancreatic acinar cells. Since DIDS had no effect on steady-state pHi the anion exchanger is unlikely to play a role in pHi regulation. However, rat pancreatic acini secrete a NaCl-rich fluid and the Cl- -HCO3- a exchanger might function in parallel with Na+-H+ exchangers to provide a mechanism for chloride accumulation across the basolateral membrane of the acinar cells.