Secretin stimulates HCO3(-) and acetate efflux but not Na+/HCO3(-) uptake in rat pancreatic ducts.
Pancreatic ducts secrete HCO3(-), but transport mechanisms are unresolved and possibly vary between species. Our aim was to study the intracellular pH (pHi) regulation and thus H+/HCO3- transport in rat pancreatic ducts. Of particular interest was the Na+/HCO3(-) cotransporter, thought to be important in HCO3(-) -transporting epithelia. pHi was measured with BCECF in freshly isolated intralobular ducts. A reduction in extracellular Na+ concentration or application of HOE 694 (1 microM) decreased pHi by 0.1 to 0.6 pH units, demonstrating Na+/H+ exchanger activity. A reduction in extracellular Cl- concentration or addition of H2DIDS (10 microM) increased pHi by 0.1 to 0.5 pH units, demonstrating Cl-/ HCO(3)- (OH ) exchanger activity. In experimental acidosis, extracellular HCO3(-)/CO2 buffer did not increase the rate of pHi recovery, indicating that provision of HCO3(-) by the Na+/HCO3(-) cotransporter was not apparent. Most importantly, Na+/HCO3(-) cotransport was not stimulated by secretin (1 nM). In contrast, in experimental alkalosis the pHi recovery was increased in HCO3(-)/CO2 buffer, possibly due to Na+/HCO3(-) cotransport in the efflux mode. Secretin (1 nM) and carbachol (1 microM) stimulated HCO3(-) efflux, which can account for the observed HCO3(-) concentrations in rat pancreatic juice. Acetate and HCO3(-) buffers were handled similarly, indicating similar transport mechanisms in pancreatic ducts.
Novak
I
I
August Krogh Institute, University of Copenhagen, Denmark. inovak@aki.ku.dk
Christoffersen
B C
BC
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000085:Acetates / Q000493:pharmacokinetics*; D000138:Acidosis / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D010183:Pancreatic Ducts / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012633:Secretin / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013268:Stimulation, Chemical
D000085:Acetates; D001639:Bicarbonates; D018679:Cholinergic Agonists; D000644:Quaternary Ammonium Compounds; D017923:Sodium-Hydrogen Exchangers; D012633:Secretin; D002217:Carbachol; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid