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Myosin heavy chain isoforms in human extraocular muscles
Daniel Kjellgren1, Lars-Eric Thornell, Jesper Andersen
1Department of Clinical Science, Section of Ophthalmology, University of Umeå, Umeå, Sweden.
Investigative Ophthalmology & Visual Science
|March 27, 2003
Summary
Human extraocular muscles (EOMs) exhibit complex myosin heavy chain (MyHC) fiber composition, differing significantly from other species. The levator palpebrae (LP) muscle also shows distinct MyHC features compared to other EOMs and limb muscles.
Area of Science:
- Muscle physiology
- Molecular biology
- Ophthalmology
Background:
- Muscle fiber type is determined by the expression of specific myosin heavy chain (MyHC) isoforms.
- Extraocular muscles (EOMs) and the levator palpebrae (LP) muscle have unique functional demands that may influence their MyHC composition.
Purpose of the Study:
- To investigate the myosin heavy chain (MyHC) composition of human extraocular (EOM) and levator palpebrae (LP) muscle fibers.
- To compare the MyHC profiles of EOMs and LP with those of other muscle types.
Main Methods:
- Adult human EOMs and LP were analyzed using SDS-PAGE, immunoblots, and immunocytochemistry with antibodies against six MyHC isoforms.
- Myofibrillar adenosine triphosphatase (mATPase) and NADH-TR activity, along with fiber area, were determined.
Main Results:
- Human EOMs demonstrated a complex MyHC composition, with a predominance of MyHCIIa, and significant proportions of MyHCI and MyHCeom.
- A subset of fibers, particularly in the orbital layer, expressed MyHCalpha-cardiac.
- The LP muscle displayed a distinct MyHC profile, notably lacking MyHCslow tonic expression.
Conclusions:
- Human EOMs possess a highly complex fiber type and MyHC composition, significantly differentiating them from EOMs of other species.
- The LP muscle exhibits unique MyHC characteristics, setting it apart from the recti, superior oblique, and limb muscles.