Bicarbonate secretion in interlobular ducts from guinea‐pig pancreas.

Abstract

Manchester M13 9PT, UK 1. The transport of HC03-across the luminal membrane of pancreatic duct cells was studied by monitoring the luminal pH of isolated guinea-pig interlobular ducts after microinjection of an extracellular fluoroprobe, the dextran conjugate of 2'7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF-dextran). Luminal Cl-concentration was also measured by microfluorometry following microinjection of the dextran conjugates of 6-methoxy-N-(4-aminoalkyl)quinolinium bromide (ABQ-dextran) and Cl-NERF (Cl-NERF-dextran).2. When HC03-/C02 was admitted to the bath, a transient acidification of the duct lumen was observed, followed by a marked alkalinization. The latter was abolished when the luminal CF-concentration was reduced to 25-35 mm by replacement with glucuronate and may, therefore, be attributed to Cl--HC03-exchange at the luminal membrane.3. Secretin, forskolin and acetylcholine stimulated HC03-secretion into the lumen even when the luminal Cl-concentration was reduced to approximately 7 mm. Furthermore, agonistevoked HC03-secretion was not inhibited by luminal glibenclamide, dihydro-4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (H2DIDS) or 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB). These observations are not easily reconciled with HC03-transport across the luminal membrane being mediated by Cl--HC03-exchange in parallel with a Clconductance.4. Agonist-stimulated HC03-secretion was blocked by omitting Nae from the bath but not by addition of N-methyl-N-isobutylamiloride (MIA) or bafilomycin A1. This supports our previous conclusion that HC03-entry into duct cells from the extracellular fluid requires Nae but is not dependent on Na+-H+ exchange or vacuolar-type H+-ATPase activity. 5. The three actions of secretin on guinea-pig pancreatic duct cells described in this and the accompanying paper -stimulation of a relatively Cl--insensitive luminal HC03-efflux pathway, stimulation of basolateral Nae-HC03-cotransport, and lack of effect on intracellular pH -require the current model of pancreatic HC03-secretion to be modified.

Functional coupling of apical Cl−/HCO3− exchange with CFTR in stimulated HCO3− secretion by guinea pig interlobular pancreatic duct

“…Interlobular ducts (diameter 100 -150 m, length 800 -1,200 m) were isolated as described previously (19), in accordance with a protocol approved by the Nagoya University Committee on Ethical Animal Use for Experiments (21). Female Hartley guinea pigs (300 -350 g) were killed by cervical dislocation.…”

“…The pH of the duct lumen (pH L) was estimated by microfluorimetry as described previously (17,21). The lumen of sealed ducts was punctured with a double-barreled (theta-glass) micropipette.…”

The HPV16 E5 oncogene inhibits endocytic trafficking

“…It was therefore tested whether HPV16 E5 also could abolish the lowering of pH in E5-transfected C127 ®broblasts. We used video microscopy and DM-NERF coupled to dextran which is an improved probe for ratio measurements of pH along the endocytic pathway (Fagotto and Max®eld, 1994;Ishiguro et al, 1996;Lee et al, 1996;Lin et al, 1999;Rathman et al, 1996).…”

SLC26 anion exchangers of guinea pig pancreatic duct: molecular cloning and functional characterization

“…The comparatively low amino acid sequence identity among orthologous mammalian Slc26 polypeptides reflects functional differences in anion transport (9) (but see Ref. 15), suggesting that mouse Slc26a6 and human SLC26A6 might differ in their ability to secrete duct cell HCO 3 Ϫ in exchange for the low luminal [Cl Ϫ ] of the distal pancreatic duct (21). The sole, previous study of human SLC26A11 proposed its function as a sulfate uptake mechanism in endothelial cells (57), but its role in pancreatic duct is unknown.…”