The measurement and dynamic implications of thin filament lengths in heart muscle.

Robinson, Thomas F.; Winegrad, Saul

doi:10.1113/jphysiol.1979.sp012640

Cited by 85 publications

(61 citation statements)

References 23 publications

(30 reference statements)

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“…This correlation was confirmed by Kruger et al using a similar size range but different muscles [41]. It is interesting to note that the converse uf this argument is also true: in cardiac muscle, which does not have nebulin, the thin filament lengths are not exactly specified and vary by -30% [42]. The gel analyses therefore indicate that nebulin is a family of proteins varying from perhaps 700 to 900 kDa, in filaments 1.05 to 1.…”

Section: Proteitmder Hypothesis Of Nebulin Functiottsupporting

confidence: 69%

Understanding the functions of titin and nebulin

Trinick

1992

FEBS Letters

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Individual molecules of the giant muscle proteins titin and nebulin span large distances in the sarcomere. Approximately one‐third of the titin molecule forms elastic filaments linking the ends of thick filaments to the Z‐line. The remainder of the molecule is probably bound to the thick filament where it may regulate assembly of myosin and the other thick filament proteins. This region also contains a sequence similar to catalytic domains in protein kinases. Nebulin appears to be associated with thin filaments and may regulate actin assembly.

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Section: Proteitmder Hypothesis Of Nebulin Functiottsupporting

confidence: 69%

Understanding the functions of titin and nebulin

Trinick

1992

FEBS Letters

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“…This evidence, however, does not preclude there being a population of thin filaments that are longer than 2.4 Am. This nonuniformity of length is known to occur in some vertebrate muscles (14) . However, if there is a population of long, thin filaments, what happens at short sarcomere lengths?…”

Section: Discussionmentioning

confidence: 99%

Length-tension relation in Limulus striated muscle.

Walcott¹,

Dewey²

1980

The Journal of Cell Biology

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Laser diffraction techniques coupled with simultaneous tension measurements were used to determine the length-tension relation in intact, small (0.5-mm thick, 1 .0-mm wide, 20-25-mm long) bundles of a Limulus (horseshoe crab) striated muscle, the telson levator muscle . This muscle differs from the model vertebrate systems in that the thick filaments are not of a constant length, but shorten from 4.9 to -2 .0 ttm as the sarcomeres shorten from 7 to 3 ttm.In the Limulus muscle, the length-tension relation plateaued to an average maximum tension of 0.34 N/m m 2 at a sarcomere length of 6.5 ,um (Lo) to 8.0 ttm . In the sarcomere length range from 3.8 to 12 .5 ttm, the muscle developed 50% or more of the maximum tension. When the sarcomere lengths are normalized (expressed as L/Lo) and the Limulus data are compared to those from frog muscle, it is apparent that Limulus muscle develops tension over a relatively greater range of sarcomere lengths.Evidence is nearly irrefutable that, in vertebrate striated muscle, shortening of sarcomeres is accompanied structurally by a reduction in 1-band width and by a constancy of the A-band width. This observation, in addition to the evidence for the constancy of lengths of the thick and thin filaments that make up the A-and I-bands, has led to the generally accepted slidingfilament theory of muscle contraction proposed by Huxley and co-workers (10, 11) . Further support ofthis theory is the lengthtension data ofGordon et al. (9), which suggest that the amount of isometric tension developed by a vertebrate striated muscle fiber is determined by the degree of overlap of the thick and thin filaments and thus, presumably, the number of myosin bridges that can interact with actin .In one invertebrate muscle, however, it has been shown that a basic tenet of the sliding-filament model is not followed; in Limulus telson levator muscle the A-bands and constitutive thick filaments change length with sarcomere length. de Villafranca (4) was the first to report extensive changes in A-band length with sarcomere length in glycerinated Limulus muscle . This was confirmed by Dewey et al. (6), who additionally demonstrated by electron microscope observations that the shortening ofthe A-band below 5 ftm resulted from $hortening of the thick filaments. This observation was confirmed by a series of experiments in which thick filaments were isolated from muscle at different sarcomere lengths (8) . Long, thick filaments (-4.2 ttm) were isolated from muscles with long sarcomeres (8 pm), whereas short, thick filaments (-2 .9 /m) were isolated from muscle with short sarcomeres (6 lilm).Given this significant variation from the structural aspect of the vertebrate system and model, the question arises as to its 204 effect on the function of the Limulus muscle. Therefore, we have determined the length-tension diagram for Limulus telson muscle and have correlated it with structural information previously determined. MATERIALS AND METHODSAdult Limulus (20-30 cm across the carapace) were obtained from...

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“…The plateau is expected to be at least as broad or broader in cardiac than in skeletal muscles [42] on the basis of variability in thin filament lengths [43]. In contrast to skeletal muscles, which express the N2A isoform of titin, cardiac myocytes in the ventricles of mice and rats express only the N2B isoform [44], which shows no Ca 2þ -dependent binding to actin [45].…”

Section: Ca 21 -Dependent N2a -Actin Interactions Contribute To Lengtmentioning

confidence: 99%

Is titin a ‘winding filament’? A new twist on muscle contraction

et al. 2011

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Recent studies have demonstrated a role for the elastic protein titin in active muscle, but the mechanisms by which titin plays this role remain to be elucidated. In active muscle, Ca 2þ -binding has been shown to increase titin stiffness, but the observed increase is too small to explain the increased stiffness of parallel elastic elements upon muscle activation. We propose a 'winding filament' mechanism for titin's role in active muscle. First, we hypothesize that Ca 2þ -dependent binding of titin's N2A region to thin filaments increases titin stiffness by preventing low-force straightening of proximal immunoglobulin domains that occurs during passive stretch. This mechanism explains the difference in length dependence of force between skeletal myofibrils and cardiac myocytes. Second, we hypothesize that cross-bridges serve not only as motors that pull thin filaments towards the M-line, but also as rotors that wind titin on the thin filaments, storing elastic potential energy in PEVK during force development and active stretch. Energy stored during force development can be recovered during active shortening. The winding filament hypothesis accounts for force enhancement during stretch and force depression during shortening, and provides testable predictions that will encourage new directions for research on mechanisms of muscle contraction.

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The measurement and dynamic implications of thin filament lengths in heart muscle.

Cited by 85 publications

References 23 publications

Understanding the functions of titin and nebulin

Understanding the functions of titin and nebulin

Length-tension relation in Limulus striated muscle.

Is titin a ‘winding filament’? A new twist on muscle contraction

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