Cycling aggregation patterns of cytoplasmic F-actin coordinated with oscillating tension force generation

Abstract

Isometric contracting protoplasmic veins of Physarum polycephalum show cycling patterns of cytoplasmic F-actin, dependent on their oscillating contraction behaviour (minute rhythms). The process of fibrillogenesis represents a parallel arrangement of F-actin chains ("plasma filaments, microfilaments") during the isometric contraction phase. A part of the results of the present work corroborates previous results on stretch-activated veins which showed that the fibrillar form of F-actin reflects the isometric contracted state. During isometric relaxation phase, a disaggregation of the fibrillar pattern takes place and is accompanied by a deparallelisation of F-actin chains. Therefore, the isometric relaxed state of cytoplasmic actomyosin is non-fibrillar in nature. Thus, the morphologically detectable fibrillar form of cytoplasmic actomyosin, according to physiological interpretation, is solely representative of the isometric contracted state. The question whether assembly-disassembly processes, e.g. G equilibrium F-actin-transformation, play a role in the contraction-relaxation cycle is discussed.

Contractile and structural reactions to impediments of Ca2+-homeostasis in Physarum polycephalum.

“…This is in agreement with previous information derived from investigations of the normal contraction-relaxation cycle : Both during a stretch induced isometric contraction (5) as well as during the peak of the force output of a normal contraction phase (31), the ultrastructure of the cytoplasmic actomyosin fibrils is characterised by a parallel arrangement of actin filaments. Similar results concerning the normal contraction-relaxation cycle were described for the isometric contraction phase by Kamiya and coworkers (16,17).…”

“…Our present analysis of the contracture phenomenon confirms the thesis that a parallel arrangement of cytoplasmic actomyosin reflects their isometrically contracted state. It should be mentioned that this is also in accordance with a functional interpretation of the light-microscopically visible fibrillar state of cytoplasmic actomyosins in other cells, e.g., the "stress-fibrils" in tissue culture cells (4, 9), i.e., interpretations inspired from the above cited previous findings in Physarum polycephalum (5,16,17,31).…”

“…Regular intrinsic oscillating phenomena, e.g., shuttle streaming and contraction activities are suitable parameters to analyse the effects of physiological factors (30). Because of its favourable size, the first demonstration of a close relation between ultrastructure and function of cytoplasmic actomyosin fibrils was possible in this object : Kamiya's and our group succeeded in correlating changes in the ultrastructure with tensiometrically controlled stages of the spontaneous contraction-relaxation cycle (5,16,17,31). …”

Reorganization of actin in platelets stimulated by thrombin as measured by the DNase I inhibition assay.

“…Several investigators have proposed that the actin filaments are formed from unpolymerized precursors (7,10,12). Platelets are one of several systems in which actin filaments have been suggested to form in vivo (13)(14)(15)(16)(17)(18), but it has hitherto not been possible to study this process by biochemical techniques.…”

Polysaccarides-based gels and solid-state electronic devices with memresistive properties: Synergy between polyaniline electrochemistry and biology

“…[34][35][36] If the mould is induced to move by a stimulus into the surrounding environment, like the presence of polysaccharides beneath it, the motor cell permeability to K + and Cl -increases, while the Ca 2+ ions alter the membrane properties, triggering large fluxes of K + and Cl -. Moreover, the penetration of water inside or outside the motor cell changes the motor cell turgor and promotes the ionic exchanges.…”