Myosin heavy chain isoforms in human extraocular muscles.
OBJECTIVE
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.
Kjellgren
Daniel
D
Department of Clinical Science, Section of Ophthalmology, University of Umeå, Umeå, Sweden.
Thornell
Lars-Eric
LE
Andersen
Jesper
J
Pedrosa-Domellöf
Fatima
F
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008297:Male; D009210:Myofibrils / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009801:Oculomotor Muscles / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism
D000911:Antibodies, Monoclonal; D020033:Protein Isoforms; D009243:NAD; D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains