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F. Pedrosa Domellöf, D. Kjellgren, P. Stal, L. Larsson, D. Furst; Uncoordinated Expression of Myosin Heavy Chains and Myosin Binding Protein C Isoforms in Human Extraocular Muscles . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5400.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the distribution of myosin binding protein C (MyBP–C) in the human extraocular muscles (EOMs) and to correlate the myosin heavy chain (MyHC) and the MyBP–C composition of the fibers.
Samples from 17 EOMs, 3 levator palpebrae (LP) and 5 limb muscles were analyzed with SDS–PAGE or processed for immunocytochemistry with monoclonal antibodies (MAb) against MyBP–C fast, MyBP–C slow, MyHCIIa, MyHCI, MyHCsto, MyHCα–cardiac and MyHCemb.
In the limb muscle samples, fast fibers were labeled with anti–MyBP–C fast and anti–MyBP–C slow, whereas the slow fibers were immunostained with anti–MyBP–C slow only, in accordance with previous studies. In 10 EOMs samples MyBP–C fast was not detected and weak staining with anti–MyBP–C fast was seen only in a few fibers in the proximal part of two muscles. The MAb against MyBP–C slow labeled all fibers, but fibers containing MyHCI were generally more strongly stained. In the levator palpebrae immunostaining with anti–MyBP–C fast was present in some fibers labeled with anti–MyHCIIa and/or anti–MyHCeom. Neither MyBP–C fast nor MyBP–C slow was detected by SDS–PAGE in the EOMs or the LP. However, faint protein bands migrating slightly above the MyBP–C slow isoform and beneath the MyBP–C fast isoform were observed in the EOMs, but not in the limb muscle samples.
The true EOMs have a unique myofibrillar protein isoform composition reflecting their special structural and functional properties. The lack of MyBP–C fast expression and the novel bands detected by SDS–PAGE suggest the presence of novel, and perhaps unique isoforms of MyBP–C in the human EOMs.
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