Histochemical and immunohistochemical profile of human and rat ocular medial rectus muscles.
OBJECTIVE
To compare the organization of human and rat ocular medial recti muscles (MR).


METHODS
The cryosections of human and rat MR were processed for myofibrillar ATPase (mATPase), succinate dehydrogenase and glycerol-3-phosphate dehydrogenase. To reveal myosin heavy chain (MyHC) isoforms, specific monoclonal antibodies against MyHC-1/beta- slow, alpha-cardiac (-alpha), -2a, -2x, -2b, -extraocular (eom), -embryonic (-emb) and -neonatal (-neo) were applied. The MyHC gene expression was studied by in situ hybridization in human muscle.


RESULTS
The muscle fibers were arranged in two distinct layers in both species. In the orbital layer most fibers were highly oxidative and expressed fast MyHC isoforms, whereas slow and oxidative fibers expressed MyHC-1 and -alpha, some of them also MyHC-2a, -2x, -eom, very rarely -emb, and -neo. In the global layer, slow fibers with very low oxidative and glycolytic activity and three types of fast fibers, glycolytic, oxidative and oxidative-glycolytic, could be distinguished. The slow medium-sized fibers with mATPase activity stable at pH 4.4 expressed mostly MyHC-1 and -alpha in rat, while in humans they co-expressed MyHC-1 with -2b, -2x, -eom, and -neo. In both species, the fast fibers showed variable mATPase activity after preincubation at pH 9.4, and co-expressed various combinations of MyHC-2b, -2x, -2a and -eom but not -emb and -neo. MyHC-2b expressing fibers were larger and glycolytic, while MyHC-2a expressing fibers were smaller and highly oxidative in both species. To our knowledge, the present study is the first that demonstrated the expression of MyHC-2b in any of human skeletal muscles. Though the expression of MyHC genes did not correlate with the immunohistochemical profile of fibers in human MR, the expression of MyHC-2b gene was undoubtedly confirmed.


CONCLUSIONS
Rat MR represent a good model that can be applied to study human MR in experiment or disease, however certain differences are to be expected due to specific oculomotor demands in humans.
Stirn Kranjc
Branka
B
University Medical Centre, University Eye Hospital Ljubljana, Ljubljana, Slovenia. Branka.Stirn@guest.arnes.si
Smerdu
Vika
V
Erzen
Ida
I
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000328:Adult; D000818:Animals; D005260:Female; D050536:Glycerol-3-Phosphate Dehydrogenase (NAD+) / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology* / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology* / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D009801:Oculomotor Muscles / Q000166:cytology* / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013385:Succinate Dehydrogenase / Q000378:metabolism; D055815:Young Adult
D020033:Protein Isoforms; D050536:Glycerol-3-Phosphate Dehydrogenase (NAD+); D013385:Succinate Dehydrogenase; D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains