title: Exhaustive exercise--a near death experience for skeletal muscle cells?
abstract: In sports medicine, muscle enzymes in the blood are frequently used as an indicator of muscle damage. It is commonly assumed that mechanical stress disrupts plasma membrane to an extent that allows large molecules, such as enzymes, to leak into the extracellular space. However, this does not appear to fully explain changes in muscle enzyme activity in the blood after exercise. Apart from this mechanically induced membrane damage, we hypothesize that, under critical metabolic conditions, ATP consuming enzymes like creatine kinase (CK) are "volitionally" expulsed by muscle cells in order to prevent cell death. This would put themselves into a situation comparable to that of CK deficient muscle fibers, which have been shown in animal experiments to be virtually infatigable at the expense of muscle strength. Additionally we expand on this hypothesis with the idea that membrane blebbing is a way for the muscle fibers to store CK in fringe areas of the muscle fiber or to expulse CK from the cytosol by detaching the blebs from the plasma membrane. The blebbing has been shown to occur in heart muscle cells under ischaemic conditions and has been speculated to be an alternative pathway for the expulsion of troponin. The blebbing has also been seen skeletal muscle cells when intracellular calcium concentration increases. Cytoskeletal damage, induced by reactive oxygen species (ROS) or by calcium activated proteases in concert with increasing intracellular pressure, seems to provoke this type of membrane reaction. If these hypotheses are confirmed by future investigations, our current understanding of CK as a blood muscle damage marker will be fundamentally affected.
authors.affiliation: Institute of Training Science and Sport Informatics, German Sport University Cologne, Germany. Electronic address: behringer@dshs-koeln.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Behringer
authors.affiliation: Institute of Training Science and Sport Informatics, German Sport University Cologne, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Montag
authors.affiliation: Institute of Training Science and Sport Informatics, German Sport University Cologne, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Franz
authors.affiliation: Institute of Training Science and Sport Informatics, German Sport University Cologne, Germany.
authors.forename: Molly L
authors.initials: ML
authors.lastname: McCourt
authors.affiliation: Institute of Training Science and Sport Informatics, German Sport University Cologne, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Mester
authors.affiliation: School of Exercise and Health Sciences, Edith Cowan University, Joondalup, WA, Australia.
authors.forename: Kazunori Ken
authors.initials: KK
authors.lastname: Nosaka
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D016923:Cell Death; D002462:Cell Membrane / Q000378:metabolism; D003402:Creatine Kinase / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005089:Exocytosis; D000067128:Extracellular Vesicles / Q000201:enzymology; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000166:cytology*; D009132:Muscles / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D012508:Sarcolemma / Q000502:physiology; D013696:Temperature
chemical_list: D004798:Enzymes; D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate; D055372:AMP-Activated Protein Kinases; D003402:Creatine Kinase; D002118:Calcium