[The inorganic phosphate transport system in the brain and the potency as vesicular glutamate transporters].
In human and rat brains, two highly homologous proteins have been identified as brain inorganic phosphate cotransport systems: a brain-specific sodium-dependent inorganic phosphate cotransporter (BNPI) and a differentiation-associated sodium-dependent inorganic phosphate cotransporter (DNPI). However, the current evidence shows that the primary role of BNPI is to accumulate excitatory amino acid neurotransmitter glutamate into synaptic vesicles as a vesicular transporter. This is indicated by an experiment in which rBNPI cDNA-transfected PC12 cells show a highly selective uptake of L-glutamate. Taken the 82% amino acid identity of DNPI to BNPI into consideration, it is very likely that DNPI is another kind of vesicular transporter for glutamate and/or related amino acids. An earlier study on BNPI expression in rat and human forebrains describes that its gene message is almost exclusively demonstrated in the telencephalon, particularly in glutamatergic projection neurons of the cerebral cortex and hippocampus. In contrast, the regional distribution of DNPI gene message is quite different from that of BNPI in the human brain, where the DNPI gene message is largely restricted to the diencephalon, especially in the thalamus. Many neurons in the dorsal thalamus are known as glutamatergic projection neurons giving rise to the thalamocortical and/or thalamostriatal pathways. Thus, both transporter proteins would be much better neuroanatomical markers than previously utilized to identify glutamatergic neurons and to distinguish distinct subpopulations of the identified neurons. Thus, the old understanding on the organization and function of glutamatergic neuron system should be re-evaluated on the basis of the two vesicular glutamate transporter proteins. Along with this thinking, we have recently analyzed the cellular and regional localization of DNPI in the rat brain by in situ hybridization and immunohistochemistry. In this review article, we explained our results about the regional difference between DNPI and BNPI in the rat forebrain, and discussed the possible functional significance of DNPI.
Hisano
Setsuji
S
Laboratory of Neuroendocrinology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D015870:Gene Expression; D006651:Histocytochemistry; D006801:Humans; D026901:Membrane Transport Proteins; D028061:Phosphate Transport Proteins; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D028061:Phosphate Transport Proteins; D012333:RNA, Messenger; C493476:SLC17A6 protein, human; C493464:SLC17A7 protein, human; C493475:Slc17a6 protein, rat; C493466:Slc17a7 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins