ISSN:
1432-0878
Keywords:
Key words: Fiber-type transition
;
Low-frequency stimulation
;
Muscle fiber morphology
;
Myosin heavy chain isoform
;
Satellite cell
;
Rat (Wistar)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract. This study investigates morphological adaptations of rat extensor digitorum longus muscle to chronic low-frequency stimulation (10 Hz, 10 h/d, up to 61 ± 7d). During the early stimulation period (2–4 d), increased basophilia and accumulation of RNA were seen predominantly in type-IIB fibers. Putative satellite cell activation, as indicated by 3H-thymidine incorporation, was also evident during this phase. By 12 d, fiber composition remained unaltered, but there was a decrease in the cross-sectional area of the type-IIB fibers. Following 28 d of low-frequency stimulation, the percentage of type-IIB fibers decreased from 43 ± 3% to 0%, while type-IID fibers increased from 30 ± 3% to 60 ± 6%. The fraction of type-IIA fibers tended to increase (controls 19 ± 3%; stimulated 29 ± 4%), whereas that of the type-I fibers was unaltered (4 ± 1%). At this time, the cross-sectional area of type-IID fibers was unaltered, but that of type-IIA and type-I fibers increased. Further stimulation resulted in a return of type-IID fibers to control levels (23 ± 5%), and a marked increase in type-IIA fibers (45 ± 8%). The percentage of type-I fibers increased from 4 ± 1% to 8 ± 1%. Throughout each stage of chronic stimulation, there was no histological evidence of fiber degeneration and regeneration. These results indicate that, in contrast to the rabbit, chronic low-frequency stimulation-induced fiber conversion in the rat extensor digitorum longus muscle is entirely due to fiber transformation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004410050163
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