A comparison of shortening and Z line degradation in post-mortem bovine, porcine, and rabbit muscle.
TL;DR: Two kinds of structural changes occur in muscle during the first 24 hours post-mortem: a variable amount of shortening and degradation of the Z line, and at higher storage temperatures, of the M line; bovine muscle Z lines are clearly more resistant to post- autopsy degradation than porcine or rabbit Muscle Z lines.
Abstract: Ultrastructural changes in bovine, porcine, and rabbit muscle have been studied during the first 24 hours post-mortem. Samples were taken for phase and electron microscopy immediately after death, after 4, 8, and 24 hours of post-mortem storage at 2° and 37°C, and after 24 hours post-mortem at 16° and 25°C. The results show that two kinds of structural changes occur in muscle during the first 24 hours post-mortem: (a) a variable amount of shortening, this shortening occurring via a sliding of filaments in all species and at all post-mortem storage temperatures examined, and (b) degradation of the Z line, and at higher storage temperatures, of the M line also. Shortening of unrestrained muscle occurs soonest post-mortem at 37°C in all three species and is completed within four hours post-mortem in porcine and rabbit muscle and within eight hours post-mortem in bovine muscle. Post-mortem short-ening of unrestrained rabbit and porcine muscle is greatest at 37°C (sarcomere lengths of 1.5 μ); shortening of rabbit muscle is minimal at 2°C (sarcomere lenght of 1.7 μ), but shortening of porcine muscle is minimal at 25°C (sarcomere length of 1.8 μ) and is slightly greater at 2°C (sarcomere length of 1.6 μ) than at 16°C. Post-mortem shortening of bovine muscle is greatest at 2°C (sarcomere length of 1.3 μ), is minimal at 16–25°C (sarcomere length of 1.8 μ), and increases between 25–37°C (sarcomere length of 1.5 μ at 37°C). Sarcomere length measurements show that some variation occurs in the extent of post-mortem shortening within the same muscle.
Z line degradation occurs sooner post-mortem and to a greater extent at storage temperatures of 25°C or above than at temperatures of 16°C or below. Also, bovine muscle Z lines are clearly more resistant to post-mortem degradation than porcine or rabbit muscle Z lines. Loss of fibrillar structure in porcine or rabbit muscle Z lines occurs during the first four hours post-mortem at 37°C, but eight hours of post-mortem storage at 37°C are required to cause loss of fibrillar structure of bovine muscle Z lines. After 24 hours at 25 or 37°C, Z lines of rabbit and porcine muscle are usually completely absent; M lines are also frequently absent in this muscle.
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01 Jan 1985
TL;DR: The sections in this article are: Fiber Composition in Human Skeletal Muscle, Motor Unit Recruitment, Adaptive Response, and Significance of Adaptation.
891 citations
TL;DR: The sections in this article are:============\/\/\/\/\/\/£££1.11\/\/£2.10\/\/£3\/\/£4\/\/£5\/\/£6.1\/\/£7.2\/\/£8\/\/£9\/\/£10\/\/ £1.7\/\/£11.5\/\/ £2.9\/\/ £3£3£4£4 £6.2£5.3£7\/\/ £7.4£8£9.5£10.2 £7======
Abstract: The sections in this article are:
1
Motor Unit
1.1
Fibers per Motor Unit
1.2
Contractile Properties
1.3
Biochemical Basis for Differences in Twitch Properties
1.4
Histochemical Differentiation of Muscle Fibers
1.5
Ultrastructural Basis for Skeletal Muscle Fiber Typing
1.6
Maximal Contractile Force
1.7
Speed of Contraction
1.8
Fatigue Characteristics
1.9
Metabolic Characteristics
1.10
Ionic Composition of Skeletal Muscle
1.11
Summary
2
Muscle Fiber Composition in Human Skeletal Muscle
3
Motor-Unit Recruitment
4
Adaptive Response in Skeletal Muscle
4.1
Muscle Size
4.2
Metabolic Capacity
5
Connective Tissue
6
Capillaries
6.1
Methodology
6.2
Anatomy
6.3
Capillary Density
6.4
Capillary Length and Diameter
6.5
Use and Disuse
6.6
Regulation
7
Significance of Adaptation
7.1
Muscular Size
7.2
Substrate Stores
7.3
Enzyme Activities
7.4
Summary
863 citations
TL;DR: Electron microscope studies described in this paper show that, during the first 3 or 4 d of postmortem storage at 4 degrees C, both costameres and N2 lines are degraded.
Abstract: A number of studies have suggested that Z-disk degradation is a major factor contributing to postmortem tenderization. These conclusions seem to have been based largely on experimental findings showing that the calpain system has a major role in postmortem tenderization, and that when incubated with myofibrils or muscle strips, purified calpain removes Z-disks. Approximately 65 to 80% of all postmortem tenderization occurs during the first 3 or 4 d postmortem, however, and there is little or no ultrastructurally detectable Z-disk degradation during this period. Electron microscope studies described in this paper show that, during the first 3 or 4 d of postmortem storage at 4 degrees C, both costameres and N2 lines are degraded. Costameres link myofibrils to the sarcolemma, and N2 lines have been reported to be areas where titin and nebulin filaments, which form a cytoskeletal network linking thick and thin filaments, respectively, to the Z-disk, coalesce. Filamentous structures linking adjacent myofibrils laterally at the level of each Z-disk are also degraded during the first 3 or 4 d of postmortem storage at 4 degrees C, resulting in gaps between myofibrils in postmortem muscle. Degradation of these structures would have important effects on tenderness. The proteins constituting these structures, nebulin and titin (N2 lines); vinculin, desmin, and dystrophin (three of the six to eight proteins constituting costameres); and desmin (filaments linking adjacent myofibrils) are all excellent substrates for the calpains, and nebulin, titin, vinculin, and desmin are largely degraded within 3 d postmortem in semimembranosus muscle. Electron micrographs of myofibrils used in the myofibril fragmentation index assay show that these myofibrils, which have been assumed to be broken at their Z-disks, in fact have intact Z-disks and are broken in their I-bands.
602 citations
TL;DR: This is the first report of a protein endogenous to muscle that is able to catalyze degradation of the myofibril, and the very low level of unbound Ca2+ in muscle cells in vivo may regulate activity of this protein fraction, or alternatively, thisprotein fraction may be localized in lysosomes.
Abstract: Removal of rabbit psoas strips immediately after death and incubation in a saline solution containing 1 mM Ca2+ and 5 nM Mg2+ for 9 hr at 37°C and pH 7.1 causes complete Z-line removal but has no ultrastructurally detectable effect on other parts of the myofibril. Z lines remain ultrastructurally intact if 1 mM 1,2-bis-(2-dicarboxymethylaminoethoxy)-ethane (EGTA) is substituted for 1 mM Ca2+ and the other conditions remain unchanged. Z lines are broadened and amorphous but are still present after incubation for 9 hr at 37°C if 1 mM ethylenediaminetetraacetate (EDTA) is substituted for 1 mM Ca2+ and 5 mM Mg2+ in the saline solution. A protein fraction that causes Z-line removal from myofibrils in the presence of Ca2+ at pH 7.0 can be isolated by extraction of ground muscle with 4 mM EDTA at pH 7.0–7.6 followed by isoelectric precipitation and fractionation between 0 and 40% ammonium sulfate saturation. Z-line removal by this protein fraction requires Ca2+ levels higher than 0.1 mM, but Z lines are removed without causing any other ultrastructurally detectable degradation of the myofibril. This is the first report of a protein endogenous to muscle that is able to catalyze degradation of the myofibril. The very low level of unbound Ca2+ in muscle cells in vivo may regulate activity of this protein fraction, or alternatively, this protein fraction may be localized in lysosomes.
344 citations
TL;DR: In this article, myofibril fragmentation index (MFI) and Warner-Bratzler (W-B) values were determined quantitatively by measuring the absorbance of a myoftibril suspension, and it was observed that MFI increased during postmortem storage for L and ST, but increased only slightly for PM.
Abstract: Samples were removed from bovine longissimus (L), semitendinosus (ST) and psoas major (PM) muscles at 1, 2, 3, 6, 7, 10 or 13 days postmortem stored at 2°C or 25°C. Myofibril fragmentation index (MFI) and Warner-Bratzler (W-B) shear-force values were determined on steaks from each muscle. Myofibril fragmentation index (MFI) was determined quantitatively by measuring the absorbance of a myofibril suspension. It was observed that MFI increased during postmortem storage for L and ST, but increased only slightly for PM. These results paralleled those changes in myofibrils observed with phase and polarized light microscopy. Both MFI and W-B shear-force values changed greatly from 1 to 3 days postmortem with a lesser change occurring after 3 days in L and ST muscles. In PM muscle, however, only a slight change in MFI and W-B shear-force occurred during postmortem storage. Elevated storage temperature (25°C) caused an accelerated change in both MFI and W-B shear-force in L and ST muscles; however, storage temperature had little effect on PM muscle. L and ST muscles responded similarly to postmortem storage, but PM muscle was characteristically different from the L and ST muscles. These findings demonstrate the differences and similarities of muscles to postmortem storage and further elucidate the role of myofibrillar proteins in meat tenderness.
314 citations
References
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TL;DR: Isolated fresh beef muscles have been found to shorten more at 2° than at 37° and three different beef muscles show this effect but two rabbit muscles do not.
Abstract: Isolated fresh beef muscles have been found to shorten more at 2° than at 37°. Minimum shortening occurs in the temperature region of 14–19°. At higher temperatures shortening coincides with the onset of rigor mortis but at low temperatures it begins rapidly and usually immediately. This shortening is reversible. Three different beef muscles show this effect but two rabbit muscles do not.
547 citations
223 citations
TL;DR: In this article, it was shown that during the aging of fiber pieces prepared from bovine sternomandibularis muscles, a loss of adhesion occurs between adjacent myofibrils.
Abstract: SUMMARY— During the aging of fiber pieces prepared from bovine sternomandibularis muscles, a loss of adhesion occurs between adjacent myofibrils. This is evidenced by increased readiness of fiber pieces to distintegrate into individual myofibrils during a period of standard disruption. Alterations also appear within the myofibrils themselves in the regions of the Z lines, sometimes leading to the apparent dissolution of this structure. Ethylenediamine tetraacetate present in the suspensions during storage not only prevents these changes, but also preserves the refractory character of the fiber pieces. Meat aging is considered therefore to be due to disruption and possible dissolution of Z-line material, leading to a weakening of inter-myofibrillar linkages probably located at the junctions of adjacent Z lines, and to loss of tensile strength of the myofibrils themselves.
141 citations
TL;DR: Postmortem shortening was accompanied by banding-pattern changes similar to those predicted for contracting muscle by Huxley and Hanson's sliding filament model and, in supercontracted myofibrils, caused a return of the banding pattern of resting muscle.
Abstract: Bovine semitendinosus muscles were sampled immediately after death, after 24 hr postmortem with storage at 2°, 16°, or 37°C, and after 312 hr postmortem with storage at 2° and 16°C. A biopsy technique was used to prevent shortening during glutaraldehyde fixation. Postfixation in osmium tetroxide was followed by embedding in an Epon-Araldite mixture. Bovine muscle was supercontracted after 24 hr storage at 27deg; but was only slightly contracted after storage at 16° for 24 hr. Muscle held at 37° for 24 hr was slightly less supercontracted than the 2° muscle. Striking similarities existed between muscles stored at 16° and at 2°C for 312 hr. Both were slightly shortened with narrowed I bands and an area of increased density, probably due to overlap of thin filaments in the middle of the A band. Postmortem shortening was accompanied by banding-pattern changes similar to those predicted for contracting muscle by Huxley and Hanson's sliding filament model. Treatment of myofibrils with 0.05% trypsin resulted in a rapid loss of Z lines and, in supercontracted myofibrils, caused a return of the banding pattern of resting muscle.
103 citations