Autowave Electromechanical Activity of the Physarum polycephalum Plasmodium
The aim of the work is to clarify the role of the electrical activity of the Physarum polycephalum plasmodium in control of the contractile activity and in self-organization of the directed locomotion. This single-celled organism with non-excitable membrane is a classic object used in studies of amoeboid motility. It exhibits patterns of motile behavior common with many tissue cells and has the same signal systems. Presence of 50 mM KCl within the agar substrate under one half of the separate plasmodial strand strongly inhibits formation of the frontal zone and leads to the sharp morphological polarization of the strand what suggests participation of electrical processes in the auto wave self-organization of the plasmodial structure. Gigantic sizes of the plasmodium allow registering its electrical activity simultaneously at different parts of the cell. It was established that potentials and currents at distant from each other parts of the plasmodium oscillate synchronously differing only in the shape of the signals, probably because of the distinction of phases or number of excited harmonics. Using the classical patch-clamp technique we recorded currents (~50 pA) of single ion channels of the plasmodial membrane. It was found that in the spectrum of current oscillations generated by the plasmodium there are high frequency fluctuations, which are probably connected with periodical detachments of membrane from cytoskeleton during formation and growth of pseudopodia. Also it was shown that neomycin, substrate inhibitor of phospholipase C, stops oscillations of both mechanical and electrical activity of plasmodia. This is consistent with its well-established ability to inhibit mechanosensitive Ca2+ channels, which are apparently present in the plasmodial membranes. The data obtained suggest that common signal systems linked with dynamics of membrane-cytoskeleton association could be involved in the galvano- and chemo-taxis of amoeboid cells.