Enrichment of fibrillar cytoplasmic actomyosin in protoplasmic strands of Physarum polycephalum for the production of cell-free models.

The treatment of isolated protoplasmic strands of Physarum polycephalum with 2.5% ethanol in a physiological salt solution under isometric conditions induces the formation of a large amount of mostly longitudinally organized actomyosin fibrils in the endoplasmic channel, a region normally free of actomyosin fibrils. The quantity of fibrillogenesis as well as the concomitant force output during the induced contractures are dependent on the Ca++-content and the temperature of the test solution. The method was developed to optimize the structure of the plasmodial strands before their subsequent transformation into cell-free models by permeabilization and extraction of the strands. Cryosections of plasmodial strands containing cytoplasmic actomyosin fibrils stained with fluorescently labeled phallotoxins offer a further assay for the study of their contraction physiology under cell-free conditions.