Author/Editor		Stirn-Kranjc, Branka; Sketelj, Janez; D'Albis, Anne; Eržen, Ida
Title		Long-term changes in myosin heavy chain composition after botulinum toxin A injection into rat medial rectus muscle
Type		članek
Source		Invest Ophthalmol Vis Sci
Vol. and No.		Letnik 42, št. 13
Publication year		2001
Volume		str. 3158-64
Language		eng
Abstract		Purpose. To study long-term changes of extraocular muscles after botulinum toxin (Botx) A-induced paralysis, with special emphasis on myosin heavy chain (MyHC) isoform pattern in muscle fibers. Methods. Botx A (5 IU) was injected into the ocular medial rectus (MR) muscles of adult rats. After 1, 5, and 8 months muscle cross sections were examined immunohistochemically, histochemically, and morphometrically. MyHC content was analyzed by gel electrophoresis. Results. Paralyzed MR muscles displayed mildly atrophic and hypertrophic muscle fibers and decreased oxidative metabolism, due to decreased succinate dehydrogenase activity. However, muscle morphology was not grossly disturbed. MyHC profile was shifted toward slower isoforms. Electrophoretic analysis showed that the share of MyHCI, and especially of MyHCII and MyHCIIx/d, increased several fold, whereas the share of MyHCIIb decreased heavily during the first 5 months. Immunohistochemical analysis generally mirrored the results obtained by electrophoresis. Moreover, specific extraocular MyHC isoform MyHCeom disappeared and could not be detected during the whole experimental period. The portion of MyHCIIb relatively increased 8 months after Botx A injection, although the MyHC profile was still far from normal. Conclusions. These long-lasting changes in Botx A-paralyzed ocular MR muscles most probably reflect their inability to regain their unique functional characteristics after new motor end plate formation and recovery of muscle contraction.
Descriptors		MYOSIN HEAVY CHAINS BOTULINUM TOXIN TYPE A OCULOMOTOR MUSCLES RATS, WISTAR IMMUNOHISTOCHEMISTRY ELECTROPHORESIS, AGAR GEL