Reactivation of cytoplasmic actomyosin in Physarum plasmodia extracted with glycerol and dimethylsulphoxide

Thin-spread plasmodia of Physarum were subjected to extraction procedures using 50% glycerol or DMSO (dimethylsulphoxide) followed by labelling of actin with fluorescent phallotoxins. During the reactivation of the actomyosin system by 2 mM-MgATP fluorescent actin fibres contract isotonically, which results in numerous fluorescent 'contraction beads'. After short-term extraction 1 mM-Ca2+ has an inhibitory effect on the reactivation. This calcium sensitivity is abolished after long-term extraction with glycerol. Calcium at 10 mM irreversibly inhibits reactivation, irrespective of the duration of extraction. The inhibitory effect of 10 mM-calcium is prevented by phallotoxin labelling prior to incubation in Ca2+. The DMSO model shows an improvement in structural preservation when compared with the glycerol models. However, reactivation is inhibited by prolonged treatment with DMSO.