Direct test of the positive pressure gradient theory of pseudopod extension and retraction in amoebae

Characteristics of motive force derived from trajectory analysis of Amoeba proteus

We used a monochromatic charge-coupled-device camera to observe the migration behavior of Amoeba proteus every 5 s over a time course of 10000 s in order to investigate the characteristics of its centroid movement (cell velocity) over the long term. Fourier transformation of the time series of the cell velocity revealed that its power spectrum exhibits a Lorentz type profile with a relaxation time of a few hundred seconds. Moreover, some sharp peaks were found in the power spectrum, where the ratios of any two frequencies corresponding to the peaks were expressed as simple rational numbers. Analysis of the trajectory using a Langevin equation showed that the power spectrum reflects characteristics of the cell's motive force. These results suggest that some phenomena relating to the cell's motility, such as protoplasmic streaming and the sol-gel transformation of actin filaments, which seem to be independent phenomena and have different relaxation times, interact with each other and cooperatively participate in the generation process of the motive force.

Chaotic behavior in the locomotion of Amoeba proteus

The locomotion of Amoeba proteus has been investigated by algorithms evaluating correlation dimension and Lyapunov spectrum developed in the field of nonlinear science. It is presumed by these parameters whether the random behavior of the system is stochastic or deterministic. For the analysis of the nonlinear parameters, n-dimensional time-delayed vectors have been reconstructed from a time series of periphery and area of A. proteus images captured with a charge-coupled-device camera, which characterize its random motion. The correlation dimension analyzed has shown the random motion of A. proteus is subjected only to 3-4 macrovariables, though the system is a complex system composed of many degrees of freedom. Furthermore, the analysis of the Lyapunov spectrum has shown its largest exponent takes positive values. These results indicate the random behavior of A. proteus is chaotic and deterministic motion on an attractor with low dimension. It may be important for the elucidation of the cell locomotion to take account of nonlinear interactions among a small number of dynamics such as the sol-gel transformation, the cytoplasmic streaming, and the relating chemical reaction occurring in the cell.

Axoplasm architecture and physical properties as seen in the Myxicola giant axon

A technique is described for extracting axoplasm from the giant axon of a marine worm, Myxicola infundibulum. The operation can be completed in 10 sec. 2. Axoplasm is pulled from the axon of a living worm as a long, clear cylinder, up to 35 cm long and 70 mg wet weight. The worm regenerates a new giant axon in about 4 months. 3. Myxicola axoplasm is a gel, 87% water, held together by protein neurofilaments. It contains small amounts of mitochondria and vesicles, but no detectable microtubules. 4. The internal structure of the gel is superficially similar to that of yarn. Closer inspection with light and electron microscopy, and X-ray diffraction, show it to be organized in a hierarchy of helical forms. Squid giant axons have a similar structure. 5. Initial estimates of the bulk physical properties of extracted Myxicola axoplasm give: breaking strength, 1400 g/cm2; specific gravity, 1-05 g/cm3; birefringence, 1-6 X 10(-4); index of refraction, 1-351; resistivity, 57 omega cm. These average values are shown to be compatible with the observed structure and composition. 6. Despite its mechanical strength, the axoplasm gel is so hydrated that Na+, K+ and homarine diffuse through it at rates approaching those in free solution. Fewer than about 5% of each of these ions are tightly bound to the gel. 7. It is argued that (a) the structure and physical properties of Myxicola axoplasm are representative of those in other axons, (b) the compound helix architecture results from twist of parallel, cross-linked fibrous proteins, and (c) this sturcture serves as a flexible internal skeleton for nerve cell processes.

Low frequency electric field induced changes in the shape and motility of amoebas

Perpendicular and parallel elongation of the giant amoeba, Chaos chaos (Chaos carolinensis), have been observed in alternating electric fields over a wide frequency range (from about 1 hertz to about 10 megahertz). The characteristics change as a function of frequency. Simple dielectric forces may be important in the production of these effects.