T. Usui et al., Functional and molecular evidence for Na+-HCO3- cotransporter in human corneal endothelial cells, PFLUG ARCH, 438(4), 1999, pp. 458-462
Although bicarbonate transport in corneal endothelium has been suggested to
be coupled to Na+, the underlying molecular mechanism has not been clarifi
ed. In the present study we investigated whether a recently cloned Na+-NCO3
- cotransporter (NBC-I) is responsible for this process, and, if so, whethe
r the endothelium expresses a separate isoform or one of the other two isof
orms that have recently been identified (kNBC-1 from kidney and pNBC-1 from
pancreas). Using primers designed for specific and common regions we demon
strated by reverse transcriptase polymerase chain reaction (RT-PCR) that bo
th kNBC-1 and pNBC-1 are expressed in cultured human corneal endothelial ce
lls. In addition functional studies with a pi-I-sensitive fluorescence prob
e were performed. In the presence of HCO3-/CO2 a pH regulatory process was
demonstrated which depends on the presence of Na+ and membrane potential, b
ut is independent of Cl- and is inhibited by the disulfonic stilbene DIDS.
These results support the presence of NBC-I as the major bicarbonate transp
ort system in corneal endothelium.