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Myosin heavy chain isoforms in human extraocular muscle
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
2003 (English)In: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, Vol. 44, no 4, 1419-1425 p.Article in journal (Refereed) Published
Abstract [en]

PURPOSE: To investigate the myosin heavy chain (MyHC) composition of human extraocular (EOM) and levator palpebrae (LP) muscle fibers. METHODS: Adult human EOMs and LP were studied with SDS-PAGE, immunoblots, and immunocytochemistry, with antibodies against six MyHC isoforms. Myofibrillar adenosine triphosphatase (mATPase) and reduced nicotinamide adenine dinucleotide (NADH)-TR activity and fiber area were also determined. RESULTS: Most of the fibers in both layers stained strongly with anti-MyHCIIa. Approximately 14% of the fibers in the global layer and 16% in the orbital layer were labeled with anti-MyHCI. The remaining 24% of the fibers in the global layer and 3% in the orbital layer were not stained with either of these two antibodies, but were reactive to anti-MyHCeom (MyHCeom(pos)/MyHCIIa(neg) fibers). The fibers stained with anti-MyHCI had acid-stable mATPase activity, and the remainder of the fibers had alkaline-stable mATPase activity. Almost all the slow fibers stained with both anti-MyHCI and anti-MyHCslow tonic in both layers. Anti-MyHCalpha-cardiac stained approximately 26% of these slow fibers in the orbital layer and 7% in the global layer. Some slow fibers in both layers lacked staining with anti-MyHCslow tonic or with anti-MyHCalpha-cardiac. MyHCemb and/or MyHCeom were also present in some of the fibers of all the groups. The LP did not stain with anti-MyHCslow tonic. CONCLUSIONS: The present study revealed that the human EOMs have a very complex fiber type and MyHC composition and differ significantly from the EOMs of other species. The features of the LP were distinct from those of the four recti, the obliquus superior, and the limb muscles.

Place, publisher, year, edition, pages
Association for Research in Vision and Ophthalmology , 2003. Vol. 44, no 4, 1419-1425 p.
Keyword [en]
extraocular musles
National Category
Ophthalmology Cell and Molecular Biology
Research subject
Human Anatomy; Ophtalmology
Identifiers
URN: urn:nbn:se:umu:diva-3935DOI: 10.1167/iovs.02-0638PubMedID: 12657575Local ID: 744OAI: oai:DiVA.org:umu-3935DiVA: diva2:142849
Available from: 2004-05-05 Created: 2004-05-05 Last updated: 2013-12-12Bibliographically approved
In thesis
1. Human extraocular muscles: molecular diversity of a unique muscle allotype
Open this publication in new window or tab >>Human extraocular muscles: molecular diversity of a unique muscle allotype
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Introduction: The extraocular muscles (EOMs) are considered a separate class of skeletal muscle, allotype. Myosin is the major contractile protein in muscle. The myosin heavy chain (MyHC) isoforms are the best molecular markers of functional heterogeneity of muscle fibers. The relaxation rate, reflects the rate at which Ca2+ is transported back into the sarcoplasmic reticulum (SR) mostly by SR Ca2+ATPase (SERCA). Myosin binding protein C (MyBP-C), plays a physiological role in regulating contraction. The laminins (Ln) are the major non-collagenous components of the basement membrane (BM) surrounding muscle fibers and are important for muscle fiber integrity.

Methods: Adult human EOMs were studied with SDS-PAGE, immunoblots and immunocytochemistry, the latter with antibodies against six MyHC, 2 SERCA, 2 MyBP-C and 8 laminin chain isoforms. The capillary density was also determined.

Results: Most fibers contained a mixture of MyHC isoforms. Three major groups of fibers could be distinguished. Fast fibers that stained with anti-MyHCIIa, slow fibers that stained with anti-MyHCI and MyHCeompos/MyHCIIaneg-fibers that stained with neither of these antibodies but with anti-MyHCI+IIa+eom and anti-MyHCeom. A majority of the fibers contained both SERCA1 and 2 whereas 1% were unstained with both antibodies. Biochemically SERCA2 was more abundant than SERCA1. MyBP-Cfast was not present in the EOMs and MyBP-Cslow was only detected immunocytochemically. The extrasynaptical BM of the EOM muscle fibers contained Lna2, b1, b2, g1, a4 and a5 chains. The capillary density in the EOMs was very high (1050 +/-190 capillaries/mm2) and significantly (p<0.05) higher in the orbital than in the global layer.

Conclusions: The co-existence of complex mixtures of several crucial protein isoforms provide the human EOMs with a unique molecular portfolio that a) allows a highly specific fine-tuning regime of contraction and relaxation, and b) imparts structural properties that are likely to contribute to protection against certain neuromuscular diseases.

Place, publisher, year, edition, pages
Umeå: Umeå university, 2004. 51 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 890
Keyword
Ophtalmology, extraocular, muscle, myosin, protein c, laminin, serca, immunocytochemistry, human, Oftalmiatrik
National Category
Ophthalmology
Research subject
Ophtalmology
Identifiers
urn:nbn:se:umu:diva-260 (URN)91-7305-638-3 (ISBN)
Public defence
2004-05-28, E04, 6E, Norrlands Universitetssjukhus, Umeå, 13:15
Opponent
Supervisors
Available from: 2004-05-05 Created: 2004-05-05 Last updated: 2011-04-08Bibliographically approved

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Kjellgren, DanielThornell, Lars-EricPedrosa-Domellöf, Fatima

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