Prolonged aestivation causes little change in skeletal muscle morphology or contractile performance in the anuran Cyclorana aloboguttata

Prolonged immobilisation or unloading of skeletal muscle causes muscle disuse atrophy that is characterised by a reduction in muscle cross-sectional area and compromised locomotory function. Animals that enter seasonal dormancy, such as hibernators and aestivators, exhibit a decline in metabolic and locomotor activity that is correlated with seasonal fluctuations in temperature and resource availability. As such, hibernators and aestivators provide a fascinating natural model for investigating muscle atrophy associated with disuse (see review by Hudson and Franklin, 2002). Previous research has also indicated that aerobic muscles should be more susceptible to muscle disuse atrophy than glycolytic muscles as there is a greater change in daily activity. We investigated the effect of aestivation on ileofibularis (relatively slow twitch) and sartorius (relatively fast twitch) muscle morphology and contractile function in C. alboguttata over a longer, more ecologically relevant time-frame of nine months. We found that whole muscle mass, muscle cross-sectional area, fibre number and proportions of fibre types remained unchanged after prolonged disuse. There were significant reductions in ileofibularis fibre cross-sectional area (> 35%) and sartorius fibre density (44%) and significant slowing of isometric kinetics. However, the work loop power output of both muscles from nine-month aestivating C. alboguttata were maintained at control levels. The results from this study strongly support the supposition that C. alboguttata is able to inhibit the effects of atrophy during disuse in both sartorius and ileofibularis muscles