Developmental Changes in the Neutral α‐Amino Acid Transport Systems of Rat Brain Over the First Three Weeks After Birth

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Abstract
Transport of 7 different amino acids into brain slices increased as donor rats aged from 1-6 days. Uptakes of 2-aminoisobutyric acid [AIB], 2-(methylamino)isobutyric acid [MeAIB] and L-alanine then decreased by day 14, while uptakes of other amino acids continued to increase or remained fairly constant. Neutral .alpha.-amino acid transport systems were characterized by measuring inhibition of uptakes and kinetics for representative amino acids at different ages. Results indicate that AIB and MeAIB used only one (and the same) system in brain slices from 6 day old rats with characteristics of system A (the major Na-dependent system in most mammalian cells). They used at least 2 systems at ages 1, 14 and 23 days, but, of these, only at 1 day did they use the same systems in the same proportions. Alanine and leucine used > 1 system at all 4 ages, and somewhat different combinations than used by each other or by AIB or MeAIB. Their transport characteristics showed they used mostly system ASC (a Na-dependent system distinguished from A) and/or system L (Na-independent). System A increases as the brain ages from 1-6 days and declines thereafter. System L probably increases with aging from 1-23 days.