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Chapter 8 Assembly of the Sarcoplasmic Reticulum during Muscle Development

1985; Elsevier BV; Linguagem: Inglês

10.1016/s0070-2161(08)60330-5

1875-6492

David H. MacLennan, Elizabeth E. Zubrzycka‐Gaarn, A O Jorgensen,

Adipose Tissue and Metabolism

This chapter focuses on the assembly of the sarcoplasmic reticulum during muscle development. The sarcoplasmic reticulum membrane from mammalian or avian skeletal muscle, like a number of other membrane systems whose synthesis has been successfully probed, has certain unique features that recommend its study. The membrane has relatively few major proteins, all of which have been well characterized with respect to their location and orientation within the membrane. Advances in recombinant DNA technology may open the potential for a genetic approach to the assembly of the sarcoplasmic reticulum. The sarcoplasmic reticulum is an organelle system wholly contained within muscle cells, where it functions in the control of intracellular free Ca2+ concentrations. It is composed of about one-third phospholipid and neutral lipids and two-thirds protein and carries out a differentiated function in muscle cells. The precursors to multinucleated myotubes—the myoblasts or satellite cells—do not have an extensive organellar network for the control of Ca2+, yet such a network develops in multinucleated myotubes. The combined biochemical and morphological studies described so far have shown that there is a gradual increase of the Ca2+ transport system in microsomal vesicles during development. Extracellular Ca2+ is an important determinant of the fusion of myoblasts in culture to form myotubes. If medium Ca2+ is kept below a concentration of a few hundred micromolar, fusion is inhibited. This observation has led to a variety of experiments in which manipulation of fusion has been studied as a determinant of differentiation.