Fluid secretion in interlobular ducts isolated from guinea-pig pancreas.
1. Pancreatic HCO3- and fluid secretion were studied by monitoring luminal pH (pHL) and luminal volume simultaneously in interlobular duct segments isolated from guinea-pig pancreas. The secretory rate and HCO3- flux were estimated from fluorescence images obtained following microinjection of BCECF-dextran (70 kDa, 20 microM) into the duct lumen. 2. Ducts filled initially with a Cl--rich solution swelled steadily (2.0 nl min-1 mm-2) when HCO3-/CO2 was introduced, and the luminal pH increased to 8.08. When Cl- was replaced by glucuronate, spontaneous fluid secretion was reduced by 75 %, and pHL did not rise above 7.3. 3. Cl--dependent spontaneous secretion was largely blocked by luminal H2DIDS (500 microM). We conclude that, in unstimulated ducts, HCO3- transport across the luminal membrane is probably mediated by Cl--HCO3- exchange. 4. Secretin (10 nM) and forskolin (1 microM) both stimulated HCO3- and fluid secretion. The final value of pHL (8.4) and the increase in secretory rate (1.5 nl min-1 mm-2) after secretin stimulation were unaffected by substitution of Cl-. 5. The Cl--independent component of secretin-evoked secretion was not affected by luminal H2DIDS. This suggests that a Cl--independent mechanism provides the main pathway for luminal HCO3- transport in secretin-stimulated ducts. 6. Ducts filled initially with a HCO3--rich fluid (125 mM HCO3-, 23 mM Cl-) secreted a Cl--rich fluid while unstimulated. This became HCO3--rich when secretin was applied. 7. Addition of H2DIDS and MIA (10 microM) to the bath reduced the secretory rate by 56 and 18 %, respectively. Applied together they completely blocked fluid secretion. We conclude that basolateral HCO3- transport is mediated mainly by Na+-HCO3- cotransport rather than by Na+-H+ exchange.
Internal Medicine II, Nagoya University School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466, Japan.
H
H
Ishiguro
S
S
Naruse
M C
MC
Steward
M
M
Kitagawa
S B
SB
Ko
T
T
Hayakawa
R M
RM
Case
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D010042:Ouabain / Q000494:pharmacology; D010183:Pancreatic Ducts / Q000378:metabolism*; D010189:Pancreatic Juice / Q000378:metabolism*; D012996:Solutions
D001639:Bicarbonates; D002712:Chlorides; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D012996:Solutions; D010042:Ouabain; D000255:Adenosine Triphosphate