Type IV collagen and laminin in slow and fast skeletal muscle in rats--effects of age and life-time endurance training.

The changes in the biochemical composition of basement membrane (BM) in slow-twitch (m. soleus, MS) and fast-twitch (m. rectus femoris, MRF) skeletal muscles of rats were studied during aging and life-time endurance training (treadmill running). The concentrations of the 7S domain of type IV collagen and of the P2 fragment of laminin were determined with radioimmunoassays in the muscles of rats aged 1, 2, 4, 10, and 24 months. The concentration of type IV collagen was higher in MS than in MRF and increased significantly with age. At older ages, the concentration tended to be higher in the MS of trained than untrained rats. The concentration of laminin was significantly higher in MRF than in MS, especially in old age. Consequently, the ratio of type IV collagen to laminin was significantly higher in MS than in MRF, the difference increasing with advancing age. The results show that the BMs in slow muscle are much more collagenous than those in fast muscle which contains, on the contrary, a higher concentration of laminin. This difference seems only partly to be explained by the higher capillarization of slow twitch muscle fibers. Aging and training seem further to distinguish the composition of the BM in slow and fast muscle.