Type and regional diversity in the distribution of myosin heavy chains in XXXX intrafusal muscle fibers.

@entity1 @entity1573 @entity35374
BACKGROUND: @entity1573 intrafusal fibers were classified on the basis of their @entity35374 ( @entity35374 ) composition, which was compared to that of @entity1 nuclear bag and nuclear chain types. METHODS: Immunoreactivities of intrafusal fibers from leg muscles of 8-week-old @entity1573 were evaluated in serial cross-sections after incubation with monoclonal antibodies against slow-twitch, slow-tonic, or fast-twitch @entity35374 and fast muscle C-protein. RESULTS: Four categories of slow intrafusal fiber could be distinguished on the basis of differential expression of slow-twitch and slow-tonic @entity35374 . Segregation into types was most evident at the motor axon supplied pole, followed by the sensory region of the equator. Fiber types were least distinct at the juxtaequator where sensory and motor axons meet. Intrafusal fibers negative for slow myosins reacted with anti-fast myosins. Fast fibers were best viewed as a single group without subdivisions. Immunostaining for fast muscle C-protein paralleled in large part reactivities for neonatal/fast @entity35374 , indicating that proteins other than @entity35374 are useful fiber type markers. CONCLUSIONS: Despite regional changes along the length of intrafusal fibers and some variation within fiber types, the concept of separate @entity35374 -based fiber types was valid as long as typing of fibers was restricted to the proximal polar region. Comparisons of @entity35374 profiles revealed similarities between @entity1573 fast intrafusal fibers and @entity1 nuclear chain fibers and between some @entity1573 slow intrafusal fibers and @entity1 nuclear bag fibers.
