Skeletal Muscle Amino Acid Transporter mRNA Expression Is Increased In Young And Older Humans Following Resistance Exercise

Abstract

INTRODUCTION: Amino acid availability is important for increasing muscle protein synthesis. However, for amino acids to be taken up and utilized by the cell, adequate transport of amino acids must occur. Interestingly, amino acid transporters have been linked to mTOR cellular signaling- a major regulator of muscle protein synthesis. PURPOSE: Therefore, we evaluated the expression levels of select amino acid transporters in young and older humans following a single bout of heavy resistance exercise. METHODS: Young (n=5) and Older (n=5) male subjects participated in a single bout of resistance exercise. Muscle biopsies were sampled at Basal, 6 and 24h post exercise. Muscle biopsies were analyzed for LAT1/SLC7A5, CD98/SLC3A2, SNAT2/SLC38A2 and PAT1/SLC36A1 mRNA expression utilizing real-time PCR. RESULTS: LAT1, CD98 and PAT1 mRNA expression were significantly elevated at 6h post in young and older subjects. However, LAT1 response was greater and was prolonged (24h) for the older subjects. Additionally, SNAT2 mRNA expression was elevated at 6 and 24h post in the older while unchanged for the younger subjects. CONCLUSIONS: These data support a rapid upregulation of amino acid transporters gene expression which may support enhanced protein synthesis following a bout of exercise. However, the robust and sustained transporter expression in the old may reflect a greater export of amino acids due to accelerated protein breakdown and muscle remodeling. Supported by ACSM Research Endowment Grant (MJD), P30 AG-024832 (MJD) and NIH/NIAMS grant R01 AR049877 (BBR)