Effect of metabolic inhibitors on phenylalanine influx in cerebral cortex slices from mature and immature rats.

Earlier investigations have shown that the transport of aromatic amino acids into cerebral cortex slices of rats changes during ontogenetic development. In order to illuminate the possible influence of the developmental alterations of energy metabolism in the brain on the changes of the amino acid transport the influx of phenylalanine into cerebral cortex slices of adult and 7-day-old rats was measured in the presence of metabolic inhibitors. Also the levels of lactate, ATP, ADP, AMP and creatine phosphate in the slices were measured. The used inhibitors cyanide, dinitrophenol and iodoacetate, which disturb certain steps of energy metabolism, had very similar effects in both age groups on phenylalanine influx and on the levels of energy-rich phosphates. The correlation between the level of ATP and the influx of phenylalanine was positive in both age groups, but the slopes of the regression lines were different. If ATP supplies energy for amino acid transport, its utilization, rather than its availability is a limiting factor in the slices from 7-day-old rats. Developmental changes in energy metabolism seem to have a minimal role in the changes of amino acid transport during the maturation of the brain. Changes in the properties of cell membrane carriers and in the transmembrane ionic gradients may be more important.