The autowave electromechanical activity of the Physarum polycephalum plasmodium

详细

The aim of this work is to clarify the role of the electrical activity of the Physarum polycephalum plasmodium in the control of the contractile activity and self-organization of the directed locomotion. This single-celled organism with a non-excitable membrane is a classic object that is used in studies of amoeboid motility. Its patterns of motor behavior and signal systems are common for many tissue cells. The presence of 50 mM KCl in an agar substrate under half of a separate plasmodial strand strongly inhibits the formation of the frontal zone and leads to sharp morphological polarization of the strand, which suggests the involvement of electrical processes in the autowave self-organization of the plasmodial structure. The gigantic sizes of the plasmodium make it possible to record its electrical activity simultaneously at different parts of the cell. It has been established that potentials and currents at parts of the plasmodium that are distant from each other oscillate synchronously and differ only in the shape of the signals, probably due to differences in the phases or the number of excited harmonics. We recorded currents (~50 pA) of single ion channels of the plasmodial membrane using the classical local voltage-clamp method. It has been found that the oscillation spectrum of the current that is generated by the plasmodium has high-frequency fluctuations, which are probably connected with periodic detachments of the membrane from the cytoskeleton during the formation and growth of the pseudopodia. It has been also shown that neomycin, a substrate inhibitor of phospholipase C, prevents oscillations of both the mechanical and electrical activity of the plasmodium. This is consistent with its well-established ability to inhibit mechanosensitive Ca²⁺ channels, which are apparently present in the plasmodial membrane. These data indicate the presence of a general signal system that is linked with the dynamics of the membrane- cytoskeleton association, which could be involved in the galvano- and chemotaxis of amoeboid cells.