Accumulation of intracellular HCO3‐ by Na(+)‐HCO3‐ cotransport in interlobular ducts from guinea‐pig pancreas.

Abstract

1. Short segments of interlobular duct were microdissected from guinea-pig pancreas following enzymatic digestion. After overnight culture, intracellular pH (pH1) and Na+ concentration ([Na+]1) were measured by microfluorometry in duct cells loaded with either the pH-sensitive fluoroprobe 2'7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) or the sodium-binding benzofuran isophthalate (SBFI).2. The transporters responsible for maintaining pHi above equilibrium were investigated by using the NH4C1 pulse technique to acid load the cells. In the absence of HCO3-/CO2, the recovery of pHi was Na+ dependent, abolished by 0-2 mm amiloride and by 10 am N-methyl-N-isobutylamiloride and was therefore attributed to Na+-H+ exchange.3. In the presence of HC03-/CO2, amiloride only partially inhibited the recovery from acid loading. The amiloride-insensitive component was abolished by 0 5 mm H2DIDS and unaffected by depletion of intracellular Cl-and was therefore attributed to Na+-HCO03 cotransport.4. Stimulation with 10 nm secretin did not cause a significant change in pHi despite a significant increase in HC03-efflux. However, in the presence of secretin, addition of 0 5 mm H2DIDS caused a decline in pHi that was three times more rapid than that obtained with 0-2 mm amiloride.5. In secretin-stimulated ducts, Na+ uptake increased when HC03-/CO2 was added to the bath and this increase was strongly inhibited by 0.5 mm H2DIDS. 6. We conclude that Na+-HCO -cotransport contributes approximately 75% of the HC03-taken up by guinea-pig pancreatic duct cells during stimulation with secretin. It is proposed that electrical coupling between HC03-efflux at the luminal membrane and electrogenic

ANG-2 for quantitative Na+ determination in living cells by time-resolved fluorescence microscopy

“…However, the global fluorescence decay analysis of the recorded 2P-FLIM images did not unravel Na + -dependent changes (data not shown). Although this calibration procedure has been successfully applied in living cells previously, 7,32 an appropriate drug combination for sufficient control of the Na + gradient across the plasma membrane could not be established for the cockroach salivary glands.…”

The distribution and expression of CFTR restricts electrogenic anion secretion to the ileum of the brushtail possum, Trichosurus vulpecula

“…As a result, following stimulation of CFTR, the intracellular Cl -activity ([Cl -]i) rapidly falls and approaches its equilibrium value, thus there is no driving force for Cl -exit across the apical membrane via CFTR (Ishiguro et al, 2002a). However, through the activity of the basolateral NaHCO 3 cotransporter and, to a lesser extent, hydration of CO 2 , the intracellular HCO 3 -activity ([HCO 3 -]i) is maintained above its equilibrium value and so HCO 3 -is secreted via CFTR (Ishiguro et al, 1996;Ishiguro et al, 2002b). In addition, it has recently been demonstrated that there is a change in selectivity of CFTR associated with stimulation of HCO 3 -secretion, with P HCO3 :P Cl increasing from 0.3-0.5 to 1.5 (Park et al, 2010).…”

Sodium-Coupled Bicarbonate Transporters

“…Based on known va lues of [ Na + ] i , pH i and V m , they concluded that the stoichiometry must be 1:2. Others subsequently described inwardly directed electrogenic Na/HCO 3 cotransporters in several mammalian cells, including pancreatic duct cells [20,21]; we functionally identified it in rat astrocytes [22]. Kurtz [23], as well as our group [24], cloned the "pancreatic" NBCe ( Figure 2: NBCe1-B), which is a splice variant of NBCe1-A.…”