Alterations in bovine skeletal muscle desmin and the cytoskeleton induced by temperature and electrical stimulation

Alterations in the myofibrillar integrating cytoskeleton and its constituent protein, desmin, were assessed in bovine skeletal muscle at 1, 24 and 168 hours of postmortem storage. Changes assessed over post-mortem storage in muscle subjected to usual (control) storage conditions (2(DEGREES)C) were compared to changes in tissue subjected to either of two conditions known to increase meat tenderness, i.e. high temperature (25(DEGREES)C) storage or electrical stimulation. Quantities of desmin extractable at the selected intervals were determined in part by densitometric scanning of the desmin band in polyacrylamide tube gels of desmin-enriched fractions. Alterations in the protein were assessed with immunoautoradiographic slab gel labelling of selected protein fractions generated during the desmin-enriching protocol with monospecific anti-desmin antibodies. Results indicate that accelerated solubilization from the cytoskeleton and subsequent breakdown of desmin occur in both storage regimes associated with accelerated tenderization of bovine skeletal muscle. High temperature promotes tenderization by favoring conditions more acceptable to proteolysis, while electrical stimulation accelerates tenderization by combined physical disruption of muscle ultrastructure and activation of muscle proteases. A highly insoluble 22,000 dalton polypeptide, not related to any myofibrillar proteins with known Z line location, appeared in desmin-enriched extracts concurrent to the breakdown of desmin in muscle stored under conditions of all three experimental regimes;Desmin was shown by immunofluorescent labelling of bovine skeletal myofibrils to be a part of a filamentous cytoskeletal network interconnecting myofibrils at the level of the Z line. The location of this cytoskeleton was not altered over 168 hours of storage in any of the experimental regimes;The arrangement of desmin into cytoskeletal filaments of 100 (ANGSTROM) diameter was unequivocally demonstrated in bovine skeletal muscle for the first time with immunoelectron microscope labelling of skeletal muscle myofibrils. These filaments had diameters that were similar to those formed from purified bovine desmin in vitro under suitable conditions of pH and ionic strength