Effect of insulin on protein degradation. Long-lived proteins in C2C12 myotubes were labelled with 1 μCi L[ring -3, 5-3H]-tyrosine/ml fusion medium for 48 hours. Myotubes were rinsed twice with 1 × HBSS and incubated in 1 × PC AA media for 2 hours. Myotubes were rinsed and incubated with 10-9, 10-8 and 10-5 M insulin for 8 hours. Samples were collected and percent protein degradation was calculated as described in material and methods. Values are means ± SEM from 5 different experiments performed in at least triplicates. * Represents significant difference compared to control (zero insulin).