Amino Acid Transporter Expression is Increased in Human Skeletal Muscle Following Essential Amino Acid Ingestion

Abstract

Essential amino acids (EAA) stimulate skeletal muscle mTORC1 signaling and protein synthesis in humans. It has recently been reported that amino acid transporters may play a role in the regulation of mTORC1 signaling and translation initiation. The purpose of this study was to profile the expression of several amino acid transporters in human skeletal muscle before and after the ingestion of EAA. Muscle biopsies were obtained from the vastus lateralis of 7 young adult subjects (3 male; 4 female) before and 1–3h after ingesting 10 grams of EAA. Blood and muscle samples were analyzed for leucine kinetics using stable isotopic techniques and qRT‐PCR was used to determine mRNA expression for L‐type (LAT1/SLC7A5, CD98/SLC34A2, LAT3/SLC7A7), sodium‐coupled neutral (SNAT2/SLC38A2 and SNAT4/SLC38A4), proton‐assisted (PAT1/SLC36A1 and PAT2/SLC36A2), cationic (CAT2/SLC7A2), and excitatory (EAAT1/SLC1A3) amino acid transporters. EAA ingestion increased blood leucine concentration, delivery to muscle, transport into muscle, muscle concentration and muscle protein synthesis in association with an increase in LAT1, CD98, SNAT2, and PAT1 expression during the first hour post‐ingestion (P<0.05). We conclude that an increase in EAA availability upregulates human skeletal muscle amino acid transporter expression which likely plays a key role in stimulating anabolic signaling and muscle protein synthesis.Supported by NIA P30 AG024832 (MJD) & NIAMS R01 AR049877 (BBR)