Role of Na(+)HCO(3)(-) cotransporter NBC1, Na(+)/H(+) exchanger NHE1, and carbonic anhydrase in rabbit duodenal bicarbonate secretion.
OBJECTIVE
HCO(3)(-) supply to the enterocyte is rate limiting for duodenal HCO(3)(-) secretion (J(HCO3-)). This study defines the molecular nature of the major HCO(3)(-) uptake pathways in rabbit duodenocytes and investigates their physiologic significance and regulation during basal and stimulated J(HCO3-).


RESULTS
pH gradient-driven (22)Na(+) uptake into duodenal basolateral membrane vesicles was partly HCO(3)(-) dependent, stilbene sensitive, and therefore mediated by Na(+)HCO(3)(-) cotransport, and partly HCO(3)(-) independent, Hoechst 642 sensitive, and therefore mediated by the Na(+)/H(+) exchanger isoform NHE1. Semiquantitative polymerase chain reaction (PCR) revealed high duodenal expression levels for the NBC1 isoform of the Na(+)HCO(3)(-) cotransporter gene family and NHE1. Cloning and comparison of full-length rabbit with human gastrointestinal and kidney NBC1 subtype revealed a conserved protein kinase A consensus sequence in the cytoplasmic N-terminus of the gastrointestinal NBC1. Inhibition of either Na(+)HCO(3)(-) cotransport or carbonic anhydrase reduced ouabain-sensitive J(HCO3-) in in vitro rabbit duodenal mucosae by approximately 50%, but did not affect 8-Br-cAMP-induced DeltaJ(HCO3-), suggesting cAMP-mediated up-regulation of the alternative pathway. However, inhibition of both Na(+)HCO(3)(-) cotransport and either carbonic anhydrase or NHE1 strongly reduced DeltaJ(HCO3-).


CONCLUSIONS
NBC1 and NHE1 are the major base importers in rabbit duodenocytes. Na(+)HCO(3)(-) cotransport and CO(2) hydration/Na(+)/H(+) exchange are equally important pathways for duodenal HCO(3)(-) supply and are up-regulated during cAMP-mediated stimulation.
Jacob
P
P
Department I, Eberhard-Karls University, Tübingen, Germany.
Christiani
S
S
Rossmann
H
H
Lamprecht
G
G
Vieillard-Baron
D
D
Müller
R
R
Gregor
M
M
Seidler
U
U
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D015152:Blotting, Northern; D002034:Bumetanide / Q000494:pharmacology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D004232:Diuretics / Q000494:pharmacology; D004386:Duodenum / Q000201:enzymology* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000502:physiology; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D011522:Protons; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D012979:Sodium Radioisotopes / Q000493:pharmacokinetics; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D002352:Carrier Proteins; D017931:DNA Primers; D004232:Diuretics; D004791:Enzyme Inhibitors; D006146:Guanidines; D011522:Protons; D012333:RNA, Messenger; D012979:Sodium Radioisotopes; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D002034:Bumetanide; D015124:8-Bromo Cyclic Adenosine Monophosphate; D010042:Ouabain; C093373:cariporide; D012964:Sodium; D002256:Carbonic Anhydrases; D000086:Acetazolamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid