Expression of the Na(+)-K(+)-2Cl- cotransporter BSC2 in the nervous system

Abstract

We used in situ hybridization and immunocytochemistry with polyclonal antibodies against the mouse bumetanide-sensitive Na(+)-K(+)-2Cl- cotransporter (mBSC2) to determine the location of this cotransporter in rat brain. Northern blots and in situ hybridization showed the presence of cotransporter mRNA in the brain, with an especially high level of expression in the choroid plexus (CP). Affinity-purified anti-BSC2 antibody identified proteins of 145-155 kDa on Western blot analysis and immunoprecipitation of brain and CP membrane protein. Indirect immunofluorescence demonstrated that BSC2 protein is located on the apical surface of the CP and is heterogeneously distributed in cell bodies and dendrites of neurons in the central and peripheral nervous system. The apical localization of BSC2 in the CP was confirmed by 86Rb+ uptakes in primary cultures of CP cells grown on permeable filters and confocal immunofluorescence microscopy. The apical localization of the cotransporter in CP epithelium suggests a role for the cotransporter in cerebrospinal fluid K+ homeostasis. In neurons, the cotransporter may help regulate intracellular Cl- concentration and thereby affect neuronal response to gamma-aminobutyric acid.

Molecular Physiology and Pathophysiology of Electroneutral Cation-Chloride Cotransporters

“…In epithelial cells, its expression is confined to basolateral membrane, some examples of which are gills, trachea, intestine, and renal collecting duct. The sole exception is choroid plexus, in which this cotransporter is expressed in apical membrane (326). In 1994, the same two independent research teams who cloned BSC1/NKCC2 also identified cDNA encoding the basolateral cotransporter.…”

“…The major role of these isoforms is translocation of ions from the lumen into cells to promote transepithelial transport, thus playing a key role in reabsorption of salt in the kidney. In contrast, in epithelial cells BSC2/NKCC1 is only expressed in basolateral membrane [except in choroid plexus, which exhibits expression in apical membrane (326,438)], the major function of which is to provide Cl Ϫ that are required for secretion in the apical membrane. K ϩ -Cl Ϫ cotransporters KCC1, KCC3, and KCC4 are all expressed in several epithelial cells, but precise localization of each isoform is not completely known (see below).…”

NKCC1 Phosphorylation Stimulates Neurite Growth of Injured Adult Sensory Neurons

“…The ubiquitously expressed protein NKCC1 (encoded by the slc12a2 gene), plays a "housekeeping" role in cell volume regulation. NKCC1 is an electroneutral transporter responsible for the entry of Na ϩ , K ϩ , and Cl Ϫ into the cell and is expressed in dorsal root ganglion (DRG) neurons (Plotkin et al, 1997). Its activity is believed to be primarily responsible for the high intracellular Cl Ϫ concentration, [Cl Ϫ ] i , in peripheral nervous system (Sung et al, 2000;Alvarez-Leefmans et al, 2001).…”

Cerebrospinal fluid hypersecretion in pediatric hydrocephalus

“…Consistent with this fact, there is evidence that NKCC1 mediates both outward-directed (into the CSF lumen) and inward-directed ion transport. 75,107,147 Because the ion composition of CSF is tightly regulated and maintained, 58,94,114 the bidirectional ion movement via NKCC1 might enable it to respond dynamically to physiological changes in the CSF to maintain homeostasis. In other secretory epithelia, the Ste20/SPS1-related proline-alanine-rich protein kinase (SPAK) associates with NKCC1 via a CCT-binding module in SPAK and a (R/K)FX(V/I)-binding motif in NKCC1 105 and stimulates NKCC1 via direct phosphorylation at Thr-203/Thr-207/Thr-212.…”