Distribution of NBCn2 (SLC4A10) splice variants in mouse brain

The five known Na-coupled HCO₃^- transporters (NCBTs) of the solute carrier 4 (SLC4) family play important roles in pH regulation and transepithelial HCO₃^- transport. Nearly all of the NCBTs have multiple splice variants. One particular NCBT, the electroneutral Na/HCO₃^- cotransporter NBCn2 (SLC4A10), which is predominantly expressed in brain, has three known splice variants-NBCn2-A, -B, and -C-as well as a potential variant-D. It is important to know the tissue-specific expression of the splice variants for understanding the physiological roles of NBCn2 in central nervous system. In the present study, we developed three novel rabbit polyclonal antibodies against NBCn2: (1) anti-ABCD, which recognizes all four variants; (2) anti-BD, which recognizes NBCn2-B and -D; (3) anti-CD, which recognizes NBCn2-C and -D. By western blotting, we examined the expression and distribution of NBCn2 splice variants in five brain regions: cerebral cortex, subcortex, cerebellum, hippocampus, and medulla. The expression pattern revealed with anti-ABCD is distinct from those revealed with anti-BD and anti-CD. Moreover, by using immunoprecipitation in combination with western blotting, we demonstrate that NBCn2-D does indeed exist and that it is predominantly expressed in subcortex, to a lesser extent in medulla, but at very low levels in cortex, cerebellum, and hippocampus. NBCn2-A may be the dominant variant in mouse brain as a whole, and may also dominate in cerebral cortex, cerebellum, and hippocampus. Immunohistochemistry with anti-ABCD shows that NBCn2 is highly expressed in choroid plexus, cortex, molecular layer of cerebellum, hippocampus, and some specific regions of the brainstem.