Neuronal expression of sodium/bicarbonate cotransporter NBCn1 (SLC4A7) and its response to chronic metabolic acidosis

Abstract

The sodium-bicarbonate cotransporter NBCn1 (SLC4A7) is an acid-base transporter that normally moves Na(+) and HCO(3)(-) into the cell. This membrane protein is sensitive to cellular and systemic pH changes. We examined NBCn1 expression and localization in the brain and its response to chronic metabolic acidosis. Two new NBCn1 antibodies were generated by immunizing a rabbit and a guinea pig. The antibodies stained neurons in a variety of rat brain regions, including hippocampal pyramidal neurons, dentate gyrus granular neurons, posterior cortical neurons, and cerebellar Purkinje neurons. Choroid plexus epithelia were also stained. Double immunofluorescence labeling showed that NBCn1 and the postsynaptic density protein PSD-95 were found in the same hippocampal CA3 neurons and partially colocalized in dendrites. PSD-95 was pulled down from rat brain lysates with the GST/NBCn1 fusion protein and was also coimmunoprecipitated with NBCn1. Chronic metabolic acidosis was induced by feeding rats with normal chow or 0.4 M HCl-containing chow for 7 days. Real-time PCR and immunoblot showed upregulation of NBCn1 mRNA and protein in the hippocampus of acidotic rats. NBCn1 immunostaining was enhanced in CA3 neurons, posterior cortical neurons, and cerebellar granular cells. Intraperitoneal administration of N-methyl-d-aspartate caused neuronal death determined by caspase-3 activity, and this effect was more severe in acidotic rats. Administering N-methyl-d-aspartate also inhibited NBCn1 upregulation in acidotic rats. We conclude that NBCn1 in neurons is upregulated by chronic acid loads, and this upregulation is associated with glutamate excitotoxicity.

Synaptic Glutamate Release Is Modulated by the Na+-Driven Cl−/HCO3−Exchanger Slc4a8

“…However, in view of our localization data (Jacobs et al, 2008) and unpublished data from our laboratory, Slc4a10 appears to be the more likely candidate. Similar to Slc4a10, the Na ϩ -HCO 3 Ϫ cotransporter Slc4a7, which also mediates acid extrusion, has been found to be localized to the postsynaptic side (Park et al, 2010), whereas it has been suggested that the Na ϩ /H ϩ exchanger Slc9a1 is present in presynaptic nerve endings (Jang et al, 2006;Dietrich and Morad, 2010).…”

The Divergence, Actions, Roles, and Relatives of Sodium-Coupled Bicarbonate Transporters

“…At the level of subregions of the central nervous system, NBCn1 transcripts (755) and protein (174,709) are widespread, being present in the cerebral cortex, hippocampus, subcortex, cerebellum, and olfactory bulb of rodents. NBCn1 immunoreactivity in wild-type rats and ␤-galactosidase staining of heterozygous mice with a lacZ insertion in the Slc4a7 gene shows that the highest level of NBCn1 promoter activity, at the tissue level, is in the pyramidal cell layers of the hippocampus, appearing equally robust in the CA1, CA2, and CA3 regions, and in the granule cells layer of the dentate gyrus (91,709).…”

“…NBCn1 immunoreactivity in wild-type rats and ␤-galactosidase staining of heterozygous mice with a lacZ insertion in the Slc4a7 gene shows that the highest level of NBCn1 promoter activity, at the tissue level, is in the pyramidal cell layers of the hippocampus, appearing equally robust in the CA1, CA2, and CA3 regions, and in the granule cells layer of the dentate gyrus (91,709). In these "lacZ" mice, NBCn1 promoter activity is also evident in certain regions of the cortex and the dentate nucleus of the cerebellum (91).…”

More actors in ammonia absorption by the thick ascending limb

“…It is shared by the NBCn1 protein expressed in various regions of the brain (26). This effect seems to be related, at least in part, to a higher mRNA abundance (26).…”

“…It is shared by the NBCn1 protein expressed in various regions of the brain (26). This effect seems to be related, at least in part, to a higher mRNA abundance (26). NBCn1 has also been found expressed in osteoclasts, but not in osteoblasts or osteocytes, and localized to the ruffled border facing the trabeculae, where its expression increases during metabolic acidosis, a condition known to elicit an osteoclast-dependent increase in bone resorption (28).…”