Abstract
An impaired amino acid sensing is associated with age-related loss of skeletal muscle mass. We tested whether light-load resistance exercise (LL-RE) affects postprandial amino acid transporter (AAT) expression in aging skeletal muscle. Untrained, healthy men (age: +65 years) were subjected to 13 h of supine rest. After 2 1/2 h of rest, unilateral LL-RE was conducted (leg extensions, 10 sets of 36 repetitions) at 16% 1RM Thereafter, the subjects were randomized into groups that orally ingested 40 g of whey protein either as hourly drinks (4 g per drink) (PULSE, N = 10) or two boluses (28 g at 0 h and 12 g at 7 h) (BOLUS, N = 10), or hourly isocaloric maltodextrin drinks (placebo, N = 10). Quadriceps muscle biopsies were taken at 0, 3, 7, and 10 h postexercise from both the resting and exercised leg, from which the membrane protein and mRNA expression of select AATs were analyzed by Western Blot and RT-PCR, respectively. LAT1 and PAT1 protein expression increased in response to LL-RE in the PULSE group, and SNAT2 and PAT1 protein expression increased in the BOLUS group when plasma BCAA concentration was low. In all three groups, LL-RE increased LAT1 mRNA expression, whereas a time course decrease in SNAT2 mRNA expression was observed. LL-RE increased membrane-associated AAT protein expression and mRNA expression. Altered AAT protein expression was only seen in groups that ingested whey protein, with the greatest effect observed after hourly feeding. This points toward an importance of AATs in the anabolic response following LL-RE and protein intake.