Myosin heavy chain isoform transition in ageing fast and slow muscles of the rat

Abstract

Sugiura, T., Matoba, H., Miyata, H., Kawai, Y. & Murakami, N. 1992. Myosin heavy chain isoform transition in ageing fast and slow muscles of the rat. Acta Physiol Scand144, 419423. Received 26 August 1991, accepted 3 December 1991. ISSN 0001–6772. Laboratory of Biomechanics and Physiology, Faculty of Liberal Arts, Yamaguchi University, Yamaguchi, Faculty of Integrated Arts and Sciences, Tokushima University, Tokushima, and Department of Physiology, Yamaguchi University School of Medicine, Ube, Yamaguchi, Japan. Using gradient sodium dodecyl sulphate‐polyacrylamide gel electrophoresis, myosin heavy chain (MHC) isoforms were studied in the extensor digitorum longus (EDI,) and the soleus muscles of male Wistar rats at different ages (5, 10, 20 weeks, 1 and 2 years). In the EDL muscle, four types of MHC isoforms were observed in all age groups. There was an increase in the percentage of HCIId and a concomitant decrease in the percentage of HCIIb with increasing age. No significant difference was observed in the percentages of HCI and HCIIa isoforms in all the age groups. In contrast, the soleus muscle contained two MHC isoforms, HCI and HCIIa. There was an increase in the percentage of HCI and a concomitant decrease in the percentage of HCIIa with increasing age. These results suggest that age‐related changes in the MHC isoforms in both the fast‐twitch EDI, and the slow‐twitch soleus muscles are one factor underlying the age‐related decrease in the speed of muscle contraction.