The concentrations of free magnesium and free calcium ions both increase in skeletal muscle fibres entering Rigor mortis.

Metabolic inhibitors have been used to induce rigor in mammalian muscle fibres previously injected with the Ca(2+)- and Mg(2+)-binding dye arsenazo III. The spectral changes which ensue, after the onset of rigor, indicate that a large increase in intracellular free Ca(2+) occurs (to more than 10(-4)m) but that this is preceded and accompanied by a substantial increase in free Mg(2+) concentration (to 2 mm or more) presumably as a result of the decline in the ATP concentration within the cell. Fibres in rigor have been treated with the divalent cation ionophore A23187 to enable Ca(2+) and Mg(2+) to be extracted selectively from the cell by extracelluar chelating agents.

The application of scanning confocal microscopy in cartilage research.

Scanning confocal microscopy has been used in conjunction with immunofluorescent localization to address two areas of debate in cartilage research. With the enhanced resolution and optical sectioning capability of this new technique, we have demonstrated that type IX collagen is preferentially located in an area around the chondrocyte, even in young cartilage. We have also shown that cathepsin B production is not confined to de-differentiated chondrocytes.

The kinetics of rigor onset in beef muscle fibres.

Force and stiffness were investigated as beef muscle fibre preparations entered rigor mortis. The results show that single fibres enter rigor rapidly (exhibit a small t(10-90)) whilst fibre bundles exhibit a much slower rate of entry into rigor (larger t(10-90)). The mean 'rigor time' in both cases is, however, similar.

The properties of glycerol-extracted Longissimus dorsi muscle fibres and myofibrils taken from beef carcasses during post-mortem conditioning.

Muscle samples from beef Longissimus dorsi (LD) were conditioned inv vacuo at 10°C for up to 21 days and then stored in a glycerol-extracted state at -20°C to determine how their mechanical properties were altered by the conditioning process. Muscle fibres were progressively more difficult to dissect as conditioning proceeded, but those dissected showed isometric mechanical tension in the presence of Ca(2+), relaxation in the absence of Ca(2+) and calcium sensitivity which did not vary with conditioning up to 8 days. Myofibrils prepared from the same conditioned tissue showed slight changes with conditioning time, namely an initial rise in Ca(2+)-activated ATPase followed by a later fall, a slow rise in ATPase in the absence of Ca(2+) and an increase in Ca(2+)-sensitivity.

Calcium efflux during the cold-induced contraction of mammalian striated muscle fibres.

The efflux of 45Ca from mammalian slow twitch muscle fibres has been studied to provide a measure of the concentration of free Ca2+ in the sarcoplasm. The kinetically complex early phases of washout of the isotope are succeeded by a prolonged slower phase which exhibits first-order kinetics. This later phase is accelerated by caffeine, by preventing oxidative phosphorylation and also during an isometric contraction, whether this contraction is produced by lowering the temperature or by electrical stimulation.