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Neal A. Rubinstein, Joseph Foon Yoong Hoh; The Distribution of Myosin Heavy Chain Isoforms among Rat Extraocular Muscle Fiber Types. Invest. Ophthalmol. Vis. Sci. 2000;41(11):3391-3398.
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purpose. To determine the distribution of myosin heavy chain isoforms in each
extraocular muscle (EOM) fiber type.
methods. Serial sections of adult rat EOMs were stained with isoform-specific
monoclonal antibodies against an array of myosin heavy chains.
Immunofluorescent antibody staining of whole adult rat EOMs, examined
by confocal microscopy, demonstrated the longitudinal variations of
isoforms along individual fibers.
results. Each global fiber type reacted predominantly with a single
isoform-specific antibody and showed no longitudinal variation. Two
major orbital fibers were defined, and both contained multiple myosin
heavy chains. Both orbital singly and multiply innervated fibers
stained proximal and distal to the neuromuscular junction with antibody
to embryonic myosin heavy chain, but this isoform was sharply and
completely excluded from the domain of the neuromuscular junction.
Orbital singly innervated fibers also contained the EOM-specific
isoform at the neuromuscular junction. Orbital multiply innervated
fibers did not contain the EOM-specific isoform, but additionally
contained a slow isoform along their entire length.
conclusions. Adult rat EOMs show unique fiber types with arrangements of myosin
heavy chain isoforms not seen in other skeletal muscles. Moreover,
unique cellular mechanisms must exist to target each isoform to its
proper domain along individual orbital fibers.
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