Underestimation of severity of previous whiplash injuries.

INTRODUCTION: We noted a report that more significant symptoms may be expressed after second whiplash injuries by a suggested cumulative effect, including degeneration. We wondered if patients were underestimating the severity of their earlier injury. PATIENTS AND METHODS: We studied recent medicolegal reports, to assess subjects with a second whiplash injury. They had been asked whether their earlier injury was worse, the same or lesser in severity. RESULTS: From the study cohort, 101 patients (87%) felt that they had fully recovered from their first injury and 15 (13%) had not. Seventy-six subjects considered their first injury of lesser severity, 24 worse and 16 the same. Of the 24 that felt the violence of their first accident was worse, only 8 had worse symptoms, and 16 felt their symptoms were mainly the same or less than their symptoms from their second injury. Statistical analysis of the data revealed that the proportion of those claiming a difference who said the previous injury was lesser was 76% (95% CI 66-84%). The observed proportion with a lesser injury was considerably higher than the 50% anticipated. CONCLUSIONS: We feel that subjects may underestimate the severity of an earlier injury and associated symptoms. Reasons for this may include secondary gain rather than any proposed cumulative effect.

Contraction of myofibrils in the presence of antibodies to myosin subfragment 2.

In a muscle-based version of in vitro motility assays, the unloaded shortening velocity of rabbit skeletal myofibrils has been determined in the presence and absence of affinity-column-purified polyclonal antibodies directed against the subfragment-2 region of myosin. Contraction was initiated by photohydrolysis of caged ATP and the time dependence of shortening was monitored by an inverted microscope equipped with a video camera. Antibody-treated myofibrils undergo unloaded shortening in a fast phase with initial rates and half-times comparable to control (untreated) myofibrils, despite a marked reduction in the isometric force of skinned muscle fibers in the presence of the antibodies. In antibody-treated myofibrils, this process is followed by a much slower phase of contraction, terminating in elongated structures with well-defined sarcomere spacings (approximately 1 micron) in contrast to the supercontracted globular state of control myofibrils. These results suggest that although the unloaded shortening of myofibrils (and in vitro motility of actin filaments over immobilized myosin heads) can be powered by myosin heads, the subfragment-2 region as well as the myosin head contributes to force production in actively contracting muscle.

Self-association of troponin.

Ox muscle troponin was shown by equilibrium- and velocity-sedimentation studies to undergo concentration-dependent dissociation into its constituent subunits as well as self-association in imidazole buffers, pH 6.9. The extent of troponin association was found to be strongly dependent on ionic strength and also to exhibit a dependence on pH and temperature; under conditions physiological in regard to pH, temperature and ionic strength the extent of polymerization of troponin is considerable in 2 mg/ml solutions. The ability of polymeric troponin to bind to tropomyosin has been inferred from studies of mixtures containing actin-tropomyosin and an excess of troponin over the amount required for the normal 7:1:1 actin-tropomyosin-troponin complex. These findings should be relevant to studies of reconstituted actin-tropomyosin-troponin preparations, since they signify possible chemical as well as physical differences between the gel, paracrystalline and filamentous states of the complex that result from adoption of different preparative procedures for analogues of the native thin filament.

Rabbit muscle myogen. Interactions with phosphate as the source of non-enantiography in moving-boundary electrophoresis.

Rabbit muscle myogen has been subjected to moving-boundary electrophoresis and velocity sedimentation in 0.0187 M-potassium phosphate buffer, pH7.7, I = 0.05. The ascending and descending and descending electrophoretic patterns are sufficiently non-enantiographic to suggest the existence of rapid, reversible interactions in the myogen solutions. However, no evidence of pronounced macromolecular association was obtained in velocity-sedimentation experiments. The source of the non-enantiography in electrophoresis has been traced to interactions of phosphate with components of myogen, which should therefore be considered as a mixutre, rather than a complex, of glycolytic enzymes.

Beef muscle troponin: evidence for multiple forms of troponin-T.

A method is described for the purification of troponin from beef skeletal muscle. The resultant preparation differs from the troponin of rabbit skeletal muscle in that it contains at least two forms of the tropomyosin-binding component, Troponin-T: these are designated as the 37 000 and 40 000 dalton forms of Troponin-T on the basis of sodium dodecyl sulphate gel electrophoresis. Either of these Troponin-T forms may be used to reconstitute troponin by mixing with the appropriate amounts of the calcium-binding (Troponin-C) and and actomyosin ATPase-inhibitory (Troponin-I) components. These reconstituted troponins are shown to interact with tropomyosin and also to confer full calcium sensitivity on actomyosin ATPase. Despite the existence of proteolysis in troponin preparations, the experimental evidence indicates that the smaller form of Troponin-T is not derived from the 40 000 dalton species by limited degradation. Although both species of Troponin-T have been found routinely in troponin from beef skeletal muscle, only the larger form is detected in troponin preparations from beef cardiac muscle. Further studies are required in order to clarify the functional significance and differential distribution of these multiple forms of Troponin-T.