This study provides ultrastructural evidence that myosin exists as aggregated thick filaments in both contracted and relaxed states of vertebrate smooth muscle cells.
Challenges artifactual explanations of smooth muscle ultrastructure; leaves open validation in human tissues and clinical translation.
Glycol dehydration followed by rehydration prior to conventional fixation appears to demonstrate the essential identity of the thick filaments observed in unfixed, glycol dehydrated and conventionally fixed smooth muscle. Observed differences in the solubilities of actin and myosin filaments also suggest that the thick filaments of smooth muscle are not formed by the apposition of actin filaments or by the deposition of myosin upon actin filaments. Evidence that the thick filaments of smooth muscle are not formed by an unnatural aggregation of smaller myosin aggregates or by the dissociation of myosin “ribbons” during tissue preparation is also reported. Examinations of smooth muscle contracted or relaxed by pharmacological agents appear to indicate that the myosin content of smooth muscle is aggregated into filaments in both the contracted and relaxed cell.
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Bois et al. (1974) studied this question.
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