Changes In Sarcomere Length Research Articles

Z disc ultrastructure in scutal depressor fibers of the barnacle.

The ultrastrlucture of Z discs in nonglycerinated, striated muscle fibers of the barnacle Balanus nubilus Darwin was examined in contracted, resting, and stretched preparations. At all sarcomnere lengths, the Z discs are perforated sheets comprised of "Z rimns" and "Z perforations," extending continuously across the myofibril; the dimensions of the rims and perforations change with changes in sarcomere length. Accordingly, with shortening of the sarcomere, there was an accompanying decrease in the transverse width of the Z rims and an increase in the diameter of the Z perforations.

Molecular Properties of Post‐Mortem Muscle. 6. Effect of Temperature on Protein Solubility of Rabbit and Bovine Muscle

SUMMARY– Studies were conducted to investigate the effect of temperature on the actin‐myosin interaction of rabbit and bovine muscle during rigor and post‐rigor shortening. Muscle was stored at four different temperatures (2°, 16°, 25° and 37°), corresponding to three types of post‐mortem muscle shortening: cold, minimal and high temperature. These three types of shortening are presumably related to different states of the actin‐myosin interaction in post‐mortem muscle. Post‐mortem tenderization may be the result of either actin‐myosin dissociation or F‐actin depolymerization.To detect the occurrence of either of these possible changes, two salt solutions, differing widely in their myofibrillar protein extracting abilities, were used to compare post‐mortem myofibrillar protein solubility after different times of post‐mortem storage and to provide information about the actin‐myosin complex. Myofibrillar protein solubility of both rabbit and beef muscle in 0.5M KCl, 0.1M phosphate, pH 7.4, increased markedly with increasing post‐mortem storage at temperatures up to 25deg;. Similar solubility changes were obtained with 1.1M Kl, 0.1M K phosphate, pH 7.4, but these changes were much smaller in magnitude. Solubility in both salt solutions, in general, decreased for muscle stored at 37°.Although time and temperature of post‐mortem storage caused appreciable alterations in protein solubility, these alterations could not be directly related to changes in tenderness or sarcomere length or to species differences in the effects of temperature on post‐mortem shortening. Viscosity, analytical ultracentrifugation, and ATPase assays all indicated the absence of “normal” actomyosin in all myofibrillar protein extracts in this study. It was suggested that the 1.1 M KI extracts contained G‐actomyosin, but the available evidence indicated the presence of only myosin in 3‐hr, 0.5 M KCI extracts.

Conformational changes in myocardial nuclei of rats.

Myocardial nuclei have been found to undergo a dramatic change in nuclear conformation during the contraction-relaxation cycle. This was demonstrated with electron micrographs of longitudinally and transversely oriented nuclei in contracted and relaxed fibers of rat myocardium. The contracted fibers had a mean sarcomere length of l.7µ ± 0.1µ (±1 SD), and extended fibers had a mean sarcomere length of 2.1µ ± 0.3µ. The amount of membrane wrinkling was quantified by comparing a straight-line distance of 6.64µ between two points on the nuclear membrane to the distance along the membrane (NML) between the same points. The degree of wrinkling was expressed as "redundancy" which is [(NML - 6.64)/6.64] x 100. Longitudinal sections showed a marked difference in mean length and width in the two populations of nuclei, with an axial ratio of 2.2 in the contracted, and 4.8 in the extended fibers. The most obvious difference between the two populations, however, was the nuclear membrane redundancy, which was 2.1% and 27.0% for the extended and contracted fibers, respectively. Although a difference in nuclear membrane redundancy was clear in longitudinal sections, it was not apparent in transverse sections. It is concluded that during systole myocardial nuclei become longitudinally compressed with folding of the membrane perpendicular to the long axis. The correlation of the change in sarcomere length with the change in nuclear length and membrane redundancy suggests a coupling of the nuclear membrane to some sarcomere segment.

The ultrastructure of the heart in systole and diastole. Chantes in sarcomere length.

The relations between ultrastructure and function have been examined in the canine left ventricle under known hemodynamic conditions. Left ventricles of normal dogs were fixed acutely by rapid perfusions of the coronary arteries in either diastole or systole, and also following acute ventricular distension, or potentiation of contraction. Sarcomere lengths at the midwall of the left ventricle averaged 2.07 µ at end diastole and 1.81 µ at end systole, changes that are adequate to explain the degree of normal ventricular emptying. Following marked ventricular emptying induced by postextrasystolic potentiation, sarcomeres shortened to an average of 1.60 µ; with acute ventricular distension resulting from over-transfusion, average sarcomere length in diastole increased to 2.25 µ. In each instance, sarcomere lengths correlated with the changes in sarcomere length predicted from changes in the dimensions of a thick-walled sphere. The importance of dispersion of sarcomere length within a given layer of the ventricular wall was noted and its potential significance discussed.

THE RELATIONSHIP BETWEEN MYOFILAMENT PACKING DENSITY AND SARCOMERE LENGTH IN FROG STRIATED MUSCLE

In cross-sections of single fibers from the frog semitendinosus muscle the number of thick myofilaments per unit area (packing density) is a direct function of the sarcomere length. Our data, derived from electron microscopic studies, fit well with other data derived from in vivo, low-angle X-ray diffraction studies of whole semitendinosus muscles. The data are consistent with the assumption that the sarcomere of a fibril maintains a constant volume during changes in sarcomere length. The myofilament lattice, therefore, expands as the sarcomere shortens. Since the distance between adjacent myofilaments is an inverse square root function of sarcomere length, the interaction of the thick and the thin myofilaments during sarcomere shortening may occur over distances which increase 70 A or more. The "expanding-sarcomere, sliding-filament" model of sarcomere shortening is discussed in terms of the current concepts of muscle architecture and contraction.

Histological Studies of Post‐Mortem Changes in Sarcomere Length as Related to Bovine Muscle Tenderness

SUMMARYThe effect of post‐mortem muscle contraction on ultimate tenderness was studied in muscles of 12 beef animals of similar weight and grade. State of contraction was determined by measurement of sarcomere lengths. Longissimus dorsi and semimembranosus muscles were observed. Histological samples removed at various intervals post‐mortem were treated with ethylenediaminetetraacetate (EDTA) to prevent further contraction. A phase‐contrast microscope was used to observe muscle fibers, and sareomeres were measured with a filar micrometer. Muscle contraction patterns of each animal were plotted through a 7‐day aging period. State of contraction after 7 days appeared to have a greater influence on subsequent (7 days) tenderness than did state of contraction at time of maximum rigor mortis. Although contraction did not seem to be the factor most responsible for final tenderness, it did appear to have a significant influence. Considerable lengthening of sarcomeres normally occurred during the aging period. Semimembranosus muscles routinely contracted less than longissimus dorsi muscles during rigor mortis, and were more relaxed after 7 days of aging. Semimembranosus muscles were consistently less tender than longissimus dorsi muscles at slaughter, but the reverse was usually true after 7 days.