Aging differentially affects human skeletal muscle amino acid transporter expression when essential amino acids are ingested after exercise.
OBJECTIVE
Amino acid transporters have been proposed as regulators of protein synthesis. The primary aim of this study was to determine whether amino acid transporter expression is increased in human muscle following resistance exercise (RE) coupled with essential amino acid (EAA) ingestion, and whether a differential response occurs with aging. Secondly, we aimed to compare this response to a previous study examining RE alone.


METHODS
Young (n = 7, 30 ± 2 yr) and older men (n = 6, 70 ± 2 yr) ingested EAA 1 h after RE. Muscle biopsies were obtained at rest and 3 and 6 h post exercise to examine amino acid transporter mRNA and protein expression.


RESULTS
In both age groups, RE + EAA increased mRNA of L-type amino acid transporter 1 (LAT1)/solute linked carrier (SLC)7A5, sodium-coupled neutral amino acid transporter 2 (SNAT2)/SLC38A2, and cationic amino acid transporter 1/SLC7A1 (p < 0.05). SNAT2 protein increased in young at 3 and 6 h (p < 0.05), whereas old maintained higher LAT1 protein (p < 0.05). Compared to RE alone, RE + EAA enhanced amino acid transporter expression only in young (p < 0.05).


CONCLUSIONS
RE increases muscle amino acid transporter expression in young and older adults, however, post exercise EAA ingestion enhances amino acid transporter expression only in young indicating that aging may influence the function of specific amino acid transporters.
Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, United States. jadickin@utmb.edu
Jared M
JM
Dickinson
Micah J
MJ
Drummond
Jennifer R
JR
Coben
Elena
E
Volpi
Blake B
BB
Rasmussen
D000328:Adult; D000368:Aged; D000375:Aging; D026905:Amino Acid Transport Systems / Q000235:genetics / Q000378:metabolism*; D000601:Amino Acids, Essential / Q000008:administration & dosage* / Q000097:blood; D001786:Blood Glucose / Q000032:analysis; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007930:Leucine / Q000097:blood; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012146:Rest / Q000502:physiology
D026905:Amino Acid Transport Systems; D000601:Amino Acids, Essential; D001786:Blood Glucose; D009124:Muscle Proteins; D012333:RNA, Messenger; D007930:Leucine