Skeletal muscle amino acid transporter expression is increased in young and older adults following resistance exercise.
Level 3 - non-randomized controlled study
Non-randomized comparative physiological study across age cohorts with repeated measures
PubMed 21527663 · doi:10.1152/japplphysiol.01408.2010
What was done
Thirteen young (28 ± 2 years) and 13 older adults (68 ± 2 years) completed a single bout of resistance exercise. Vastus lateralis muscle biopsies were taken at baseline and at 3, 6, and 24 hours postexercise. Samples were analyzed via real-time PCR and Western blotting for amino acid transporter mRNA and protein expression (including LAT1/SLC7A5, CD98/SLC3A2, SNAT2/SLC38A2, PAT1/SLC36A1, and CAT1/SLC7A1) as well as signaling regulators (eIF2α, rpS6, ATF4, and STAT3).
What was found
Basal amino acid transporter expression did not differ between young and older adults (P > 0.05). Resistance exercise increased mRNA expression of SLC7A5, SLC3A2, SLC38A2, SLC36A1, and SLC7A1 in both young and older adults (P < 0.05; exact numerical values not reported in abstract). However, LAT1 and CD98 protein increased only in younger adults (P < 0.05). Phosphorylated eIF2α increased postexercise in both groups (P < 0.05). Phosphorylated rpS6 and nuclear ATF4 tended to be higher in the young, while nuclear STAT3 phosphorylation was higher in older subjects postexercise (P < 0.05).
Why it matters
The findings show that while transcriptional activation of amino acid transporters following resistance exercise is preserved with aging, the translation into key transporter proteins is blunted in older muscle, potentially contributing to age-related anabolic resistance.
Limits
Sample size is small (13 per cohort). The abstract does not provide exact numerical effect sizes or confidence intervals. The study examined only acute responses up to 24 hours after a single exercise bout and did not directly measure amino acid uptake kinetics or muscle protein synthesis rates.
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