Molecular and functional evidence for electrogenic and electroneutral Na(+)-HCO(3)(-) cotransporters in murine duodenum.
Inward Na(+)-HCO(3)(-) cotransport has previously been demonstrated in acidified duodenal epithelial cells, but the identity and localization of the mRNAs and proteins involved have not been determined. The molecular expression and localization of Na(+)-HCO(3)(-) cotransporters (NBCs) were studied by RT-PCR, sequence analysis, and immunohistochemistry. By fluorescence spectroscopy, the intracellular pH (pH(i)) was recorded in suspensions of isolated murine duodenal epithelial cells loaded with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Proximal duodenal epithelial cells expressed mRNA encoding two electrogenic NBC1 isoforms and the electroneutral NBCn1. Both NBC1 and NBCn1 were localized to the basolateral membrane of proximal duodenal villus cells, whereas the crypt cells did not label with the anti-NBC antibodies. DIDS or removal of extracellular Cl(-) increased pH(i), whereas an acidification was observed on removal of Na(+) or both Na(+) and Cl(-). The effects of inhibitors and ionic dependence of acid/base transporters were consistent with both inward and outward Na(+)-HCO(3)(-) cotransport. Hence, we propose that NBCs are involved in both basolateral electroneutral HCO(3)(-) transport as well as basolateral electrogenic HCO(3)(-) transport in proximal duodenal villus cells.
Praetorius
J
J
Department of Physiology and Pharmacology, Institute of Medical Biology, University of Southern Denmark-Odense University, Winsloewparken 21, DK-5000 Odense C, Denmark. praetorj@nhlbi.nih.gov
Hager
H
H
Nielsen
S
S
Aalkjaer
C
C
Friis
U G
UG
Ainsworth
M A
MA
Johansen
T
T
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000136:Acid-Base Equilibrium / Q000187:drug effects; D000143:Acids / Q000494:pharmacology; D000468:Alkalies / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D002469:Cell Separation; D002712:Chlorides / Q000378:metabolism; D004386:Duodenum / Q000166:cytology / Q000378:metabolism*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012964:Sodium / Q000378:metabolism; D027982:Sodium-Bicarbonate Symporters; D013050:Spectrometry, Fluorescence
D000143:Acids; D000468:Alkalies; D002352:Carrier Proteins; D002712:Chlorides; D005456:Fluorescent Dyes; D020033:Protein Isoforms; D012333:RNA, Messenger; D027982:Sodium-Bicarbonate Symporters; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid