Myofibrillar-protein isoforms and sarcoplasmic-reticulum Ca2+-transport activity of single human muscle fibres.

TitleMyofibrillar-protein isoforms and sarcoplasmic-reticulum Ca2+-transport activity of single human muscle fibres.
Publication TypeJournal Article
Year of Publication1984
AuthorsSalviati, G, Betto, R, D Betto, D, Zeviani, M
JournalBiochem J
Volume224
Issue1
Pagination215-25
Date Published1984 Nov 15
ISSN0264-6021
KeywordsAge Factors, Biological Transport, Calcium, Electrophoresis, Polyacrylamide Gel, Female, Humans, Muscle Proteins, Muscles, Myofibrils, Myosins, Polymorphism, Genetic, Sarcoplasmic Reticulum
Abstract

In this study the polymorphism of myofibrillar proteins and the Ca2+-uptake activity of sarcoplasmic reticulum were analysed in single fibres from human skeletal muscles. Two populations of histochemically identified type-I fibres were found differing in the number of light-chain isoforms of the constituent myosin, whereas the pattern of light chains of fast myosin of type-IIA and type-IIB fibres was indistinguishable. Regulatory proteins, troponin and tropomyosin, and other myofibrillar proteins, such as M- and C-proteins, showed specific isoforms in type-I and type-II fibres. Furthermore, tropomyosin presented different stoichiometries of the alpha- and beta-subunits between the two types of fibres. Sarcoplasmic-reticulum volume, as indicated by the maximum capacity for calcium oxalate accumulation, was almost identical in type-I and type-II fibres, whereas the rate of Ca2+ transport was twice as high in type-II as compared with type-I fibres. It is concluded that, in normal human muscle fibres, there is a tight segregation of fast and slow isoforms of myofibrillar proteins that is very well co-ordinated with the relaxing activity of the sarcoplasmic reticulum. These findings may thus represent a molecular correlation with the differences of the twitch-contraction time between fast and slow human motor units. This tight segregation is partially lost in the muscle fibres of elderly individuals.

DOI10.1042/bj2240215
Alternate JournalBiochem. J.
Citation Key10.1042/bj2240215
PubMed ID6508759
PubMed Central IDPMC1144416