Effect of exercise and obesity on skeletal muscle amino acid uptake

To determine if amino acid uptake by muscle of the obese Zucker rat is impaired, epitrochlearis (EPI) and soleus strip (SOL) muscles from 32 pairs of female lean (Fa/-) and obese (fa/fa) Zucker rats were incubated using [14C]α-aminoisobutyric acid (AIB). Because contractile activity also influences amino acid uptake, the effect of acute endurance exercise on amino acid uptake by skeletal muscle from lean and obese rats was also studied. Muscle wet and dry weights were similar in lean and obese rats. However, both muscle protein content and concentration from obese rats were significantly reduced. In preliminary studies, pinning EPI at resting length during incubation significantly increased AIB uptake and reduced muscle water accumulation. AIB uptake was similar in stripped and intact SOL. Lean and obese rats were studied at rest or following a 1 hr treadmill run at 8% grade Muscles were pinned, and preincubated for 30 min at 37 degree C in Krebs Ringer bicarbonate buffer (KRB) containing 5mM glucose under 95:5 O2/CO2, followed by 30, 60, 120, or 180 min of incubation in KRB with 0.5 mM AIB, [14C]-AIB to measure amino acid, and [3H]-inulin to determine extracellular water