Integrity Of Myofibrils Research Articles

Effects of 12- O-tetradecanoyl-phorbol- 13-acetate on myofibril integrity and Ca 2+ content in developing myotubes

The cocarcinogen 12- O-tetradecanoyl-phorbol-13-acetate (TPA) has a prompt and selective effect on striated myofibrils in well-formed, multinucleated myotubes. The myofibrillar apparatus is totally disrupted and largely degraded after 3 days in TPA. Fluorescent-tagged antibodies to muscle-specific light meromyosin and electron microscopy document this catabolic effect of TPA. This selective degradation of fully assembled striated myofibrils is readily reversible. This reassembly of myofibrils requires de novo protein synthesis. The TPA-treated myotubes are unusually rich in autophagosomes, organelles rarely observed in normal myotubes. TPA has no discernable effect on the morphology of the subsarcolemmal microfilaments, mitochondria, microtubules, or sarcoplasmic reticulum (SR). The programmed disappearance of the fibroblast-type, intermediate 10-nm filaments (FIF) that occurs as normal myotubes mature is not altered by TPA. However, the TPA-treated myotubes depleted of myofibrils are filled with an extensive meshwork of the muscle-type intermediate 10-nm filaments (MIF). The drug has no obvious effect on the constitutive contractile proteins comprising the submembranous microfilaments, or the FIF in presumptive myoblasts or fibroblasts, nor does it affect the motility associated with these replicating cells. The striking increase in total calcium content which occurs as normal myotubes mature is absent in myotubes treated with TPA.

EFFECT OF Ca2+ ON CHANGES IN MYOFIBRILLAR PROTEINS OF BOVINE SKELETAL MUSCLE

ABSTRACTThe effects of Ca2+ on the integrity of myofibrils and their proteins were studied by isolating myofibrils from minced at‐death bovine longissimus muscle samples treated with 1 mM Ca2+ and 10 mM oxalate and stored at either 2°C or 23°C. Myofibrils were isolated from treated and control samples at various postmortem times and characterized with SDS‐polyacrylamide gel electrophoresis. In addition, myofibrils were isolated from treated and control samples at various postmortem times and extracted with Hasselbach‐Schneider (H‐S) solution and with 1 mM Tris, pH 8.5. These extracts were characterized with SDS‐polyacrylamide gel electrophoresis. Myofibrils isolated from postmortem muscle samples treated with Ca2+ showed more rapid degradation of troponin T and the concurrent appearance of a 30,000‐dalton component during postmortem storage than did control and oxalate samples. Proteins extracted from myofibrils increased during postmortem storage with both H‐S and Tris solutions. The salt soluble proteins of Ca2+ treated samples showed more 30,000‐dalton component and α‐actinin compared with control and oxalate samples. In essence, the extent and nature of changes in myofibrils and in extracted proteins were dependent upon Ca2+ availability. Storage of muscle samples at room temperature accelerated all these changes. Postmortem modifications in myofibrillar proteins were interpreted as being consonant with the hypothesis that proteolysis of myofibrils is caused by a Ca2+ ‐activated factor endogenous to the muscle fiber.

Scanning Electron Microscopy of Heated Beef, Chicken and Rainbow Trout Muscles

Abstract The effects of heating postrigor skeletal muscle from beef, chicken and rainbow trout were examined by scanning electron microscopy. With muscles heated to 97°C, the structural integrity of myofibrils was lost near or at the transverse elements. In addition, fibrils from trout muscle had transverse fissures at the level of the H zone. Granular matter was observed beneath the sarcolemma of fibers in heated beef and chicken muscles. When the sarcoplasm was removed from intact beef muscle by eentri-fugation or extraction, no granular matter was noted in the heated tissue. Heated (97°C) beef sarcoplasm had a granular appearance; the diameters of the granules were similar to those in heated intact beef muscle. Endomysial fibers were not detected in the muscles heated to 97° but in the tissue heated to 60°C, swollen fibers were apparent. Changes in muscles from beef and chicken heated to 60°C were small although extensive damage was apparent in muscle from rainbow trout.