| [ Summary ] |
BNPI was originally cloned as the first brain-specific inorganic phosphate (Pi) transporter from the rat brain. In 2000, we isolated DNPI as the second brain-specific Pi transporter. Recent transgene experiments have shown that both transporters have the ability to transport L-glutamate, as vesicular transport systems. Although these transporters share substrates, Pi and L-glutamate, expression of mRNA and immuno reactivity in the rat brain is sharply different in the regional distribution between BNPI and DNPI. BNPI and DNPI mRNAs are expressed at high levels in the telencephalon and diencephalon, respectively. In the hypothalamus, only DNPI mRNA is expressed in particular subsets of neurons including neuroendocrine neurons. Only DNPI immunoreactivity is present, in neuroendocrine terminal fields such as the median eminence and the posterior pituitary. This particular pattern of DNPI expression suggests that DNPI, unlike BNPI operates as a specific system for the transport of Pi and/or L-glutamate in the hypothalamic neuroendocrine neuron system. |