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Characterization of Na + ‐Dependent Phosphate Uptake in Cultured Fetal Rat Cortical Neurons
Author(s) -
Glinn Michele,
Ni Binhui,
Paul Steven M.
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.65052358.x
Subject(s) - cotransporter , oligomycin , extracellular , choline , cerebral cortex , chemistry , neuron , dinitrophenol , biochemistry , calcium , biophysics , biology , medicine , endocrinology , sodium , atpase , enzyme , neuroscience , organic chemistry
Our laboratory has recently cloned and expressed a brain‐ and neuron‐specific Na + ‐dependent inorganic phosphate (P i ) cotransporter that is constitutively expressed in neurons of the rat cerebral cortex, hippocampus, and cerebellum. We have now characterized Na + ‐dependent 32 P i cotransport in cultured fetal rat cortical neurons, where >90% of saturable P i uptake is Na + ‐dependent. Saturable, Na + ‐dependent 32 P i uptake was first observed in primary cultures of cortical neurons at 7 days in vitro (DIV) and was maximal at 12 DIV. Na + ‐dependent P i transport was optimal at physiological temperature (37°C) and pH (7.0–7.5), with apparent K m values for P i and Na + of 54 ± 12.7 µ M and 35 ± 4.2 m M , respectively. A reduction in extracellular Ca 2+ markedly reduced (>60%) Na + ‐dependent P i uptake, with a threshold for maximal P i import of 1–2.5 m M CaCl 2 . Primary cultures of fetal cortical neurons incubated in medium where equimolar concentrations of choline were substituted for Na + had lower levels of ATP and ADP and higher levels of AMP than did those incubated in the presence of Na + . Furthermore, a substantial fraction of the 32 P i cotransported with Na + was concentrated in the adenine nucleotides. Inhibitors of oxidative metabolism, such as rotenone, oligomycin, or dinitrophenol, dramatically decreased Na + ‐dependent P i import rates. These data establish the presence of a Na + ‐dependent P i cotransport system in neurons of the CNS, demonstrate the Ca 2+ ‐dependent nature of 32 P i uptake, and suggest that the neuronal Na + ‐dependent P i cotransporter may import P i required for the production of high‐energy compounds vital to neuronal metabolism.