SYNAPTOSOMAL TRANSPORT OF BRANCHED-CHAIN AMINO-ACIDS IN YOUNG, ADULT AND AGED RAT-BRAIN CORTEX

Uptake of branched chain amino acids (BCAA, leucine and isoleucine) wa s studied in synaptosomes prepared from the cerebral cortex of rats of 1, 3 and 24 months of age. In addition to the conventional low affini ty sodium independent transport system, a high affinity sodium depende nt stereospecific transport system for the transport of BCAA was ident ified in synaptosomes prepared from the cerebral cortex of the above t hree age groups. There was an overall decrease in K-m and V-max of bot h high and low affinity transport systems for leucine and isoleucine i n the cortical synaptosomes of 24-month-old rats when compared with yo unger age groups; This study indicates that the non-neurotransmitter e ssential amino acids are transported by high and low affinity transpor t systems and these systems undergo age-dependent alterations. These c hanges might be due to the altered synthesis of these transporter prot eins and/or synthesis of transporters with altered conformation and/or changes in the physical properties (fluidity) of the membrane. The de crease in the transport of BCAA is on a par with the decrease in the o verall metabolism of BCAA in brain. As food consumption decreases in t he older age groups of animals, the availability of essential amino ac ids to the tissues might also be lowered. Under such conditions, it is suggested that the observed increase in the affinity (decreased K-m) of the carrier might be helpful in the supply of essential amino acids .