Inorganic phosphate enhances phosphonucleotide concentrations in cultured fetal rat cortical neurons

Our laboratory has recently characterized saturable Na⁺-dependent P(i) import into cultured fetal rat cortical neurons and shown that a substantial fraction of the P(i) so accumulated is incorporated into ATP. We now report that the ATP, NADPH and intracellular free P(i) ([P(i)](i)) concentrations of cultured fetal rat cortical neurons are dependent on the extracellular P(i) concentration ([P(i)](e)). [ATP], [NADPH] and [P(i)](i) display a hyperbolic dependence upon [P(i)](e), being significantly increased after incubation with [P(i)](e) of ≤ 10 μM, and maximal at ≤ 500 μM. Increases in both [ATP] and [NADPH] are abolished in the absence of glucose. In the absence of extracellular P(i), both [ATP] and [P(i)](i) decline over time. Our data suggest that in cultured fetal rat cortical neurons [P(i)](e) has a direct effect on glucose utilization, stimulating both ATP and NADPH synthesis via glycolysis and the pentose phosphate pathway.