EXPRESSION OF THE NA-K+-2CL(-) COTRANSPORTER BSC2 IN THE NERVOUS-SYSTEM()

We used in situ hybridization and immunocytochemistry with polyclonal antibodies against the mouse bumetanide-sensitive Na+-K+-2Cl(-) cotran sporter (mBSC2) to determine the location of this cotransporter in rat brain. Northern blots and in situ hybridization showed the presence o f cotransporter mRNA in the brain, with an especially high level of ex pression in the choroid plexus (CP). Affinity-purified anti-BSC2 antib ody identified proteins of 145-155 kDa on Western blot analysis and im munoprecipitation of brain and CP membrane protein. Indirect immunoflu orescence demonstrated that BSC2 protein is located on the apical surf ace of the CP and is heterogeneously distributed in cell bodies and de ndrites of neurons in the central and peripheral nervous system. The a pical localization of BSC2 in the CP was confirmed by Rb-86(+) uptakes in primary cultures of CP cells grown on permeable filters and confoc al immunofluorescence microscopy. The apical localization of the cotra nsporter in CP epithelium suggests a role for the cotransporter in cer ebrospinal fluid K+ homeostasis. In neurons, the cotransporter may hel p regulate intracellular Cl- concentration and thereby affect neuronal response to gamma-aminobutyric acid.