CLONING AND EXPRESSION OF A CDNA-ENCODING A BRAIN-SPECIFIC NA-DEPENDENT INORGANIC-PHOSPHATE COTRANSPORTER()

We have isolated a brain-specific cDNA that encodes a Na+-dependent in organic phosphate (P-i) cotransporter (BNPI). The nucleotide sequence of BNPI predicts a protein of 560 amino acids with 6-8 putative transm embrane-spanning segments that is approximate to 32% identical to the rabbit kidney Na+-dependent P-i cotransporter. Expression of BNPI mRNA in Xenopus oocytes results in Na+-dependent P-i transport similar to that reported for the recombinantly expressed or native kidney Na+-dep endent cotransporter. RNA blot analysis reveals that BNPI mRNA is expr essed predominantly (if not exclusively) in brain, and in situ hybridi zation histochemistry reveals BNPI transcripts in neurons of the cereb ral cortex, hippocampus, and cerebellum. Furthermore, we have confirme d the presence of saturable Na+-dependent P-i cotransport in cultured cerebellar granule cells. Together, these data demonstrate the presenc e of a specific neuronal Na+-dependent transport system for P-i in bra in.