Abstract
The interlobular duct segments of guinea-pig pancreas secrete HCO3− into a HCO3−-rich (125 mM) luminal fluid following secretin stimulation. Under these conditions intracellular HCO3− is ~20 mM and intracellular potential is ~-60 mV indicating a luminally directed electrochemical gradient for HCO3−. To examine whether luminal HCO3− transport is mediated by an anion conductance, we measured changes in intracellular pH (pHi) when the cells were de- or hyper-polarized by manipulation of extracellular K+ ([K+]B). The isolated ducts were superfused with HCO3−/CO2-free solution and luminally perfused with 125 mM HCO3− and 24 mM Cl−. pHi was measured with BCECF. When [K+]B was raised from 5 to 70 mM, pHi in the unstimulated ducts changed slightly. In the presence of dbcAMP, the depolarization caused a large increase in pHi from 6.83 ± 0.11 to 7.32 ± 0.09 (mean ± SEM, n = 4, p<0.01). When [K+]B was reduced from 5 to 1 mM, pHi decreased by 0.11 ± 0.01 (p<0.05). Under Cl−-free conditions, when [K+]B was reduced from 5 to 1 mM and then raised to 70 mM in the presence of dbcAMP, pHi decreased from 7.15 ± 0.06 (n = 4) to 7.06 ± 0.07 and then increased to 7.54 ± 0.16 (p<0.05). In summary, de- and hyper-polarization caused changes in pHi that most probably reflected the influx and efflux of HCO3− across the luminal membrane. These HCO3− movements were not dependent on the presence of Cl− and may be attributed to the presence of a significant HCO3− conductance at the luminal membrane. [Jpn J Physiol 54 Suppl:S87 (2004)]
