Muscle atrophy during starvation in a marine teleost.

The marine telost Pollachius virens undergoes a natural starvation during the winter, and provides a reversible, non-pathological model for studying muscle wasting. In the present study fish were kept without food under laboratory conditions for up to 12 weeks. The effects of starvation on muscle fibre size, volume fractions of mitochondria and myofibrils, and capillary supply were determined. Starvation results in a preferential atrophy and degradation of fast muscle myofibrillar proteins. For example, fibre cross-sectional area decreased from 1014 to 535 micrometers 2 (p less than 0.005) and myofibrillar volume fraction from 79.0% to 56.4% (p less than 0.001) in fast fibres following 12 weeks starvation. In contrast there was little change in these parameters in slow muscle fibres. Evidence is presented that M-line and Z-disc breakdown occur as an initial stage of myofibrillar degradation. Sarcoplasmic reticulum in atrophied fibres often appeared swollen and multi-membraned lysosome-like vesicles were common. The percentage of slow fibres (44 to 64%; p less than 0.025) and fast fibers (51 to 86%; p less than 0.01) without capillary contact increased and the percentage of fibre perimeter vascularised decreased during a 12 week starvation (6.3 to 3.3% in slow fibres and 2.8 to 1.1% fast fibres). The volume fractions of mitochondria in slow fibres decreased in parallel to the decrease in capillary supply (from 34.6 to 18.6%; p less than 0.001). Mechanisms of myofibrillar degradation during muscle wasting are discussed.