The characean internodal cell as a model system for studying wound healing.

This work describes the characean internodal cell as a model system for the study of wound healing and compares wounds induced by certain chemicals and UV irradiation with wounds occurring in the natural environment. We review the existing literature and define three types of wound response: (1) cortical window formation characterised by disassembly of microtubules, transient inhibition of actin-dependent cytoplasmic streaming and chloroplast detachment, (2) fibrillar wound walls characterised by exocytosis of vesicles carrying wall polysaccharides and membrane-bound cellulose synthase complexes coupled with endocytosis of surplus membrane and (3) amorphous, callose- and membrane-containing wound walls characterised by exocytosis of vesicles and endoplasmic reticulum cisternae in the absence of membrane recycling. We hypothesize that these three wound responses reflect the extent of damage, probably Ca(2+) influx, and that the secretion of Ca(2+) -loaded endoplasmic reticulum cisternae is an emergency reaction in case of severe Ca(2+) load. Microtubules are not required for wound healing but their disassembly could have a signalling function. Transient reorganisation of the actin cytoskeleton into a meshwork of randomly oriented filaments is required for the migration of wound wall forming organelles, just as occurs in tip-growing plant cells. New data presented in this study show that during the deposition of an amorphous wound wall numerous actin rings are present, which may indicate specific ion fluxes and/or a storage form for actin. In addition, we present new evidence for the exocytosis of FM1-43-stained organelles, putative endosomes, required for plasma membrane repair during wound healing. Finally, we show that quickly growing fibrillar wound walls, even when deposited in the absence of microtubules, have a highly ordered helical structure of consistent handedness comprised of cellulose microfibrils.

[Interaction of melittin with ion channels of excitable membranes].

The effect of the neurotoxin melittin on the activation of ion channels of excitable membrane, the plasmalemma of Characeae algae cells, isolated membrane patches of neurons of mollusc L. stagnalis and Vero cells was studied by the method of intracellular perfusion and the patch-clamp technique in inside-out configuration. It was shown that melittin disturbs the conductivity of plasmalemma and modifieds Ca(2+)-channels of plant membrane. The leakage current that appears by the action of melittin can be restored by substituting calmodulin for melittin. Melittin modifies K(+)-channels of animal cell membrane by disrupting the phospholipid matrix and forms conductive structures in the membrane by interacting with channel proteins, which is evidenced by the appearance of additional ion channels.

Wide-ranging effects of eight cytochalasins and latrunculin A and B on intracellular motility and actin filament reorganization in characean internodal cells.

Numerous forms of cytochalasins have been identified and, although they share common biological activity, they may differ considerably in potency. We investigated the effects of cytochalasins A, B, C, D, E, H and J and dihydrocytochalasin B in an ideal experimental system for cell motility, the giant internodal cells of the characean alga Nitella pseudoflabellata. Cytochalasins D (60 microM) and H (30 microM) were found to be most suited for fast and reversible inhibition of actin-based motility, while cytochalasins A and E arrested streaming at lower concentrations but irreversibly. We observed no clear correlation between the ability of cytochalasins to inhibit motility and the actual disruption of the subcortical actin bundle tracks on which myosin-dependent motility occurs. Indeed, the actin bundles remained intact at the time of streaming cessation and disassembled only after one to several days' treatment. Even when applied at concentrations lower than that required to inhibit cytoplasmic streaming, all of the cytochalasins induced reorganization of the more labile cortical actin filaments into actin patches, swirling clusters or short rods. Latrunculins A and B arrested streaming only after disrupting the subcortical actin bundles, a process requiring relatively high concentrations (200 microM) and very long treatment periods of >1 d. Latrunculins, however, worked synergistically with cytochalasins. A 1 h treatment with 15 nM latrunculin A and 4 microM cytochalasin D induced reversible fragmentation of subcortical actin bundles and arrested cytoplasmic streaming. Our findings provide insights into the mechanisms by which cytochalasins and latrunculins interfere with characean actin to inhibit motility.

Membrane potential genesis in Nitella cells, mitochondria, and thylakoids.

The resting membrane potential of Nitella cells shifts in parallel with the change in H+ equilibrium potential, but is not equal to the H+ equilibrium potential. The deviation of the membrane potential from the H+ equilibrium potential depends on the extrusion rate of H+ by the electrogenic H+-pump. The activity of the electrogenic H+-pump was formulated in terms of the change in the free energy of ATP hydrolysis. The deviation of membrane potential from the H+ equilibrium potential induces a passive H+ flow. The passive inward H+ current may be coupled with Cl- uptake. The coupling rate of H+,Cl- co-transport was discussed. The membrane potential of mitochondria was electrochemically formulated in terms of oxidation-reduction H2/H+ half-cells spontaneously formed at the inner and outer boundaries of each trans-membrane electron-conducting pathway. The membrane potential formed by a pair of H2/H+ redox cells is pH-sensitive in its nature, but deviates from the H+ equilibrium potential to an extent that depends on the logarithm of the ratio of H2 concentrations at the inner and outer boundaries. The membrane potential of thylakoids is considered to be primarily due to the electromotive force of photocells embedded in the thylakoid membrane, as far as the anode and cathode of each photocell are in contact with the inner and outer solutions, respectively. The light-induced electronic current yields oxygen at the inner boundary and causes an increase in the H2 pool at the outer boundary of the electron-conducting pathway, which has no shunting plastoquinone chain between these two boundaries.