title: Intracellular Ca(2+)-handling differs markedly between intact human muscle fibers and myotubes.
abstract: BACKGROUND
  In skeletal muscle, intracellular Ca(2+) is an important regulator of contraction as well as gene expression and metabolic processes. Because of the difficulties to obtain intact human muscle fibers, human myotubes have been extensively employed for studies of Ca(2+)-dependent processes in human adult muscle. Despite this, it is unknown whether the Ca(2+)-handling properties of myotubes adequately represent those of adult muscle fibers.
  
  
  METHODS
  To enable a comparison of the Ca(2+)-handling properties of human muscle fibers and myotubes, we developed a model of dissected intact single muscle fibers obtained from human intercostal muscle biopsies. The intracellular Ca(2+)-handling of human muscle fibers was compared with that of myotubes generated by the differentiation of primary human myoblasts obtained from vastus lateralis muscle biopsies.
  
  
  RESULTS
  The intact single muscle fibers all demonstrated strictly regulated cytosolic free [Ca(2+)] ([Ca(2+)]i) transients and force production upon electrical stimulation. In contrast, despite a more mature Ca(2+)-handling in myotubes than in myoblasts, myotubes lacked fundamental aspects of adult Ca(2+)-handling and did not contract. These functional differences were explained by discrepancies in the quantity and localization of Ca(2+)-handling proteins, as well as ultrastructural differences between muscle fibers and myotubes.
  
  
  CONCLUSIONS
  Intact single muscle fibers that display strictly regulated [Ca(2+)]i transients and force production upon electrical stimulation can be obtained from human intercostal muscle biopsies. In contrast, human myotubes lack important aspects of adult Ca(2+)-handling and are thus an inappropriate model for human adult muscle when studying Ca(2+)-dependent processes, such as gene expression and metabolic processes.
authors: Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, 141 86 Sweden ; Department of Physiology and Pharmacology, Karolinska Institutet, von Eulers väg 8, Stockholm, 171 77 Sweden.
authors: Karl
authors: K
authors: Olsson
authors: Department of Physiology and Pharmacology, Karolinska Institutet, von Eulers väg 8, Stockholm, 171 77 Sweden.
authors: Arthur J
authors: AJ
authors: Cheng
authors: Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, 141 86 Sweden.
authors: Seher
authors: S
authors: Alam
authors: Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital Solna, Stockholm, 171 76 Sweden.
authors: Mamdoh
authors: M
authors: Al-Ameri
authors: Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, 141 86 Sweden.
authors: Eric
authors: E
authors: Rullman
authors: Department of Physiology and Pharmacology, Karolinska Institutet, von Eulers väg 8, Stockholm, 171 77 Sweden.
authors: Håkan
authors: H
authors: Westerblad
authors: Department of Physiology and Pharmacology, Karolinska Institutet, von Eulers väg 8, Stockholm, 171 77 Sweden.
authors: Johanna T
authors: JT
authors: Lanner
authors: Department of Physiology and Pharmacology, Karolinska Institutet, von Eulers väg 8, Stockholm, 171 77 Sweden.
authors: Joseph D
authors: JD
authors: Bruton
authors: Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, 141 86 Sweden.
authors: Thomas
authors: T
authors: Gustafsson
keywords: Ex vivo model; Excitation-contraction coupling; Force production; Gene expression; Human skeletal muscle; Intact human muscle fibers; Metabolic processes; Myoblasts; Satellite cells