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Journal of Biomedicine and Biotechnology
Volume 2011 (2011), Article ID 830573, 9 pages
Review Article

The Evolution of the Mitochondria-to-Calcium Release Units Relationship in Vertebrate Skeletal Muscles

1Department of Cell and Developmental Biology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
2Center for Research on Ageing and Department of Neuroscience and Imaging, Università Gabriele d'Annunzio, 66100 Chieti, Italy

Received 5 July 2011; Accepted 10 August 2011

Academic Editor: Aikaterini Kontrogianni-Konstantopoulos

Copyright © 2011 Clara Franzini-Armstrong and Simona Boncompagni. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The spatial relationship between mitochondria and the membrane systems, more specifically the calcium release units (CRUs) of skeletal muscle, is of profound functional significance. CRUs are the sites at which Ca2+ is released from the sarcoplasmic reticulum during muscle activation. Close mitochondrion-CRU proximity allows the organelles to take up Ca2+ and thus stimulate aerobic metabolism. Skeletal muscles of most mammals display an extensive, developmentally regulated, close mitochondrion-CRU association, fostered by tethering links between the organelles. A comparative look at the vertebrate subphylum however shows that this specific association is only present in the higher vertebrates (mammals). Muscles in all other vertebrates, even if capable of fast activity, rely on a less precise and more limited mitochondrion-CRU proximity, despite some tethering connections. This is most evident in fish muscles. Clustering of free subsarcolemmal mitochondria in proximity of capillaries is also more frequently achieved in mammalian than in other vertebrates.