Functional and molecular evidence for Na(+)-HCO3- cotransporter in human corneal endothelial cells.
Although bicarbonate transport in corneal endothelium has been suggested to be coupled to Na+, the underlying molecular mechanism has not been clarified. In the present study we investigated whether a recently cloned Na(+)-HCO3- cotransporter (NBC-1) is responsible for this process, and, if so, whether the endothelium expresses a separate isoform or one of the other two isoforms that have recently been identified (kNBC-1 from kidney and pNBC-1 from pancreas). Using primers designed for specific and common regions we demonstrated by reverse transcriptase polymerase chain reaction (RT-PCR) that both kNBC-1 and pNBC-1 are expressed in cultured human corneal endothelial cells. In addition functional studies with a pH-sensitive fluorescence probe were performed. In the presence of HCO3-/CO2 a pH regulatory process was demonstrated which depends on the presence of Na+ and membrane potential, but is independent of Cl- and is inhibited by the disulfonic stilbene DIDS. These results support the presence of NBC-1 as the major bicarbonate transport system in corneal endothelium.
Usui
T
T
Department of Ophthalmology, Faculty of Medicine, University of Tokyo, Japan.
Seki
G
G
Amano
S
S
Oshika
T
T
Miyata
K
K
Kunimi
M
M
Taniguchi
S
S
Uwatoko
S
S
Fujita
T
T
Araie
M
M
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004728:Endothelium, Corneal / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027982:Sodium-Bicarbonate Symporters
D002352:Carrier Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D027982:Sodium-Bicarbonate Symporters; D000643:Ammonium Chloride; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid