ISSN:
0886-1544
Keywords:
filament translation
;
insect-flight muscle
;
rigor-stretch model
;
electron microscopy
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
To investigate the pattern of actin-filament translation in the intact myofibrillar matrix, we carried out electron micrographic experiments on the “rigor-stretch” model of insect-flight muscle. In this model, thin filaments are mechanically severed from their connections to the Z-line and may then slide freely over the myosin filament when activated. The model is similar to the in vitro motility assay in that untethered actin filaments slide over myosin, but here the natural filament lattice is retained: sliding takes place through the lattice of thick filaments. We find, in this model, that while the extent of thin filament translation is variable from sarcomere to sarcomere, filaments never translate far enough to enter the opposite I-band. Unlike the in vitro motility assay, where the actin filament translates over the entire thick filament even with “incorrectly” polarized crossbridges as the sole driver, in this intact filament-lattice model, cross-bridges are apparently unable to move filaments in both directions. We also find that the pattern of filament translation is collective. Although the extent of translation may vary among sarcomeres, in any given half-sarcomere all actin filaments translate by the same degree. Further, the extent of translation is is the same in both halves of a given sarcomere. In rare instances where the extent of translation exhibited a transverse gradient across the myofibrillar half-sarcomere, the gradient was similar on both sides of the sarcomere. Filament translation within the sarcomere is thus collective. Some mechanism ensures that nearby but distinctly separated actin filaments move together and that cooperative-like behavior therefore extends to the supramolecular level.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cm.970320215
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