Comparison of contractile, histo- and biochemical properties of different skeletal muscles of the brown rat (Rattus norvegicus) with those of the domesticated Wistar rat

Abstract

1. Muscle properties of rat strains showing different locomotor activities were studied. The isometric contraction times (CT) of the slow soleus muscle are shorter in both young and adult domesticated Wistar than in wild brown rats; no difference was found in the fast extensor digitorum longus (EDL) muscles. No significant difference was seen with respect to half relaxation time (HRT) in either fast or slow muscles. CT and HRT of the diaphragm are longer in young brown rats than in domesticated animals, while the diaphragm of the adult wild rat differs only by a longer HRT. 2. Histochemically, the fast EDL muscle and diaphragm show different types of muscle fibres, i.e. fibres with low and high myofibrillar ATPase activity (type I and II), and fibres with low, intermediate and high succinic dehydrogenase (SDH) activity (type A, B and C). The EDL and diaphragm of brown rats have a higher percentage of “fast-red” fibres with high ATPase and SDH activities (type II C) and phospholipid content, than the Wistar rats. The slow soleus muscles of young and adult brown rats are uniform with respect to low ATPase activity and heterogeneous with respect to SDH activity; in the Wistar rat the soleus muscles are heterogeneous with respect to both myosin ATPase and SDH activities, i.e. they contain “slow-intermediate” (I B) and “fast-red” (II C) fibres. The pattern of phospholipid content is similar to the SDH pattern in each case. No difference was found in phosphorylase activity. The glycogen content is higher in both fast and slow muscles of the adult rat than in the muscles of the domesticated rat.