Secretin causes H+/HCO3- secretion from pig pancreatic ductules by vacuolar-type H(+)-adenosine triphosphatase.
OBJECTIVE
Secretin stimulates pancreatic ductules to secrete HCO3- into pancreatic juice and H+ into interstitial fluid. The aim of the present study was first to examine whether ductular H+ secretion is inhibited by micromolar concentrations of bafilomycin A1, which blocks vacuolar H(+)-adenosine triphosphatase by specific action, and secondly to test for evidence of ductular Na+/HCO3- cotransport.


METHODS
Ductular H+ secretion was estimated from the rate of intracellular pH recovery after acid-loading (24 mmol/L NH4Cl) microdissected pancreatic ductules from pig, mounted in a flow-through perfusion chamber on the stage of a fluorescent microscope. Intracellular pH was measured using the fluorescent pH indicator 2'7'-bis (carboxyethyl)-5,6-carboxyfluorescein and dual-wave-length excitation of fluorescence. The ducts were superfused perfused with either HCO3(-)-free HEPES-containing buffers or HCO3(-)-containing buffers.


RESULTS
Secretin (10(-8) mol/L) induced a net H+ secretion of 1.87 +/- 0.23 mumol.mL cell vol-1.min-1 that was blocked by 10(-6) mol/L bafilomycin A1 and was unaffected by Na+ substitution with choline using HEPES superfusion buffers. Secretin-stimulated ductules superfused with bicarbonate-containing, Cl(-)-free buffers showed Na(+)-dependent and 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid-inhibitable alkalinization of intracellular pH.


CONCLUSIONS
Secretin causes H+/HCO3- secretion from pancreatic ductules by a mechanism involving vacuolar-type H(+)-adenosine phosphatase. Pancreatic ductules also show Na+/HCO3- cotransport, which may account for a small fraction of secreted bicarbonate.
Villanger
O
O
Institute for Experimental Medical Research, University of Oslo, Norway.
Veel
T
T
Raeder
M G
MG
D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D002021:Buffers; D002712:Chlorides / Q000494:pharmacology; D005260:Female; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D018942:Macrolides; D008297:Male; D010183:Pancreatic Ducts / Q000187:drug effects / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D012633:Secretin / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013552:Swine
D000900:Anti-Bacterial Agents; D001639:Bicarbonates; D002021:Buffers; D002712:Chlorides; D018942:Macrolides; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; C057620:bafilomycin A; D012633:Secretin; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D006180:Proton-Translocating ATPases