title: Proximal duodenal enterocyte transport: evidence for Na(+)-H+ and Cl(-)-HCO3- exchange and NaHCO3 cotransport.
abstract: The duodenum, in contrast to the jejunum, actively secretes HCO3- at a high rate, a process that protects the mucosa from acid/peptic injury. Our purpose was to define the mechanisms involved in HCO3- transport by studying the acid-base transport processes in isolated duodenal enterocytes. Individual rat duodenocytes, isolated by a combination of Ca2+ chelation and collagenase, attached to a collagen matrix were loaded with the pH-sensitive fluoroprobe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM), and intracellular pH was monitored by microfluorospectrophotometry. To identify Na(+)-H+ transport, cells in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid 1) were pulsed with NH4Cl (40 mM) in the absence and presence of amiloride and 2) were removed of Na+. To examine Cl(-)-HCO3- exchange, Cl- was removed from Ringer-HCO3- superfusate in the presence and absence of dihydro-4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (H2DIDS). The NaHCO3 cotransporter was studied by addition and subtraction of Na+ to amiloride-treated and Cl(-)-depleted enterocytes perfused with Na(+)- and Cl(-)-free Ringer-HCO3- buffer with and without H2DIDS. Mammalian duodenocytes contain at least three acid-base transporters: an amiloride-sensitive Na(+)-H+ exchanger that extrudes acid, a DIDS-sensitive Cl(-)-HCO3- exchanger that extrudes base, and a NaHCO3 cotransporter, also DIDS sensitive, that functions as a base loader. These acid-base transporters likely play a key role in duodenal mucosal HCO3- secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology and Medical Biophysics, Uppsala University Biomedical Center, Sweden.
authors.forename: J I
authors.initials: JI
authors.lastname: Isenberg
authors.forename: M
authors.initials: M
authors.lastname: Ljungström
authors.forename: B
authors.initials: B
authors.lastname: Säfsten
authors.forename: G
authors.initials: G
authors.lastname: Flemström
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002469:Cell Separation; D002470:Cell Survival; D027963:Chloride-Bicarbonate Antiporters; D004386:Duodenum / Q000166:cytology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: D017920:Antiporters; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; C018564:dihydro-DIDS; D000584:Amiloride; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid