In neurons and glia, HCO3 transporters regulate both intracellular pH and brain extracellular pH. Except for the anion exchangers, little was known of HCO3 transporters at the molecular level until Romero et al. expression cloned the renal electrogenic Na/HCO3 cotransporter (Nature, 387:409,1997). By screening rat-brain cDNA libraries with portions of rat-kidney NBC (Romero et al., AJP, in press), we isolated a full-length and several partial-length NBC-related clones. The full-length clone, which encodes 689 amino acids and has several predicted membrane-spanning domains, is identical to rat-kidney NBC except for two unique features. First, its open reading frame (ORF) is ∼1.1 kb shorter than rat-kidney NBC at the 5′ end. Second, the novel clone has a 97 base-pair (bp) deletion near the 3′ end, causing a frameshift that would yield a protein with 61 unique C-terminal amino acids. Using RT-PCR, we confirmed the presence of these unique 5′ and 3′ ends in mRNA from rat brain. On a rat Northern blot probed with the novel 5′ UTR, we identified ∼4.5 and ∼2.8 kb messages that are present abundantly in heart, lung and kidney, moderately in brain, spleen and liver, and scarcely in skeletal muscle and testis. We generated antibodies to the unique C-terminal 46 amino acids of rat-kidney NBC, as well as to the unique C-terminal 61 amino acids of the novel NBC. On Western blots, both antibodies predominantly recognize a ∼130 kDa protein, plus two smaller 70-100 kDa proteins. The antibody to the novel NBC recognizes these proteins in rat brain, but not kidney. We conclude that several novel NBC-related proteins are expressed in rat brain.
|Original language||English (US)|
|State||Published - Mar 20 1998|
ASJC Scopus subject areas
- Molecular Biology