Rheological properties of living cytoplasm: endoplasm of Physarum plasmodium.

Abstract

Magnetic sphere viscoelastometry, video microscopy, and the Kamiya double chamber method (Kamiya, N., 1940, Science [Wash. DC], 92:462-463.) have been combined in an optical and theological investigation of the living endoplasm of Physarum polycephalum. The rheological properties examined were yield stress, viscosity (as a function of shear), and elasticity. These parameters were evaluated in directions perpendicular; (X) and parallel (Y) to the plasmodial vein. Known magnetic forces were used for measurements in the X direction, while the falling ball technique was used in the Y direction (Cygan, D. A., and B. Caswell, 1971, Trans. Soc. Rheol. 15:663-683; MacLean-Fletcher, S. D., and T. D. Pollard, 1980, J. Cell Biol., 85:414-428).Approximate yield stresses were calculated in the X and Y directions of 0.58 and 1.05 dyn/ cm 2, respectively. Apparent viscosities measured in the two directions (r/x and r/v) were found to fluctuate with time. The fluctuations in r/× and r/v were shown, statistically, to occur independently of each other. Frequency correlation with dynamoplasmograms indicated that these fluctuations probably occur independently of the streaming cycle. Viscosity was found to be a complex function of shear, indicating that the endoplasm is non-Newtonian. Plots of shear stress vs. rate of shear both parallel and perpendicular to the vein, showed that endoplasm is not a shear thinning material.These experiments have shown that living endoplasm of Physarum is an anisotropic viscoelastic fluid with a yield stress. The endoplasm appears not to be a homogeneous material, but to be composed of heterogeneous domains.Previous investigations of living cytoplasm in its many states have been crude at best. Micromanipulation (9) and various centrifuge experiments (2,8,16,19) have been informative, but disruptive to cell structure. One promising approach is the magnetic particle method (53). The pioneering attempts of Heilbronn (18) and Seifriz (50), along with the efforts of Crick and Hughes (10), Yagi (56), and Hiramoto (20) have been instrumental in the development of this technique. Although largely qualitative, these experiments have indicated that the cytoplasm of various systems is non-Newtonian. Therefore, cytoplasm can not be characterized by a single rheological parameter such as viscosity. Hiramoto's application (20) of the magnetic particle method in sea urchin eggs and Hwang's experiments (23) in mucus further established the possibility of calibrating the method.We have developed a calibrated magnetic particle technique to analyze nondisruptively, yield stress, apparent viscosity, and elasticity, in living cytoplasm. It is designed to be applied to large syncytial systems, cell extracts, and fluid volumes of 10 pl or less. The technique has been successfully applied to the endoplasm of the large acellular slime mold, Physarum polycephalum. An abundance of biochemical, ultrastructural, and biophysical information is available on Physarum (see reviews: 15, 27, 28, 31, 35, 41). In addition, t...

Mechanisms of cell shape change: the cytomechanics of cellular response to chemical environment and mechanical loading

“…In their study of Physarum endoplasm, Sato et al (1983) conclude that endoplasm is non-newtonian . They also conclude that endoplasm is not a shear thinning material, i .e., viscosity does not decrease as strain rate increases.…”

“…Less frequently examined, although equally critical, are the responses of the cell to the mechanical loads imposed on them by their cytoskeletons or by external forces (Waddington, 1942;Odell et al, 1981;Condeelis, 1983 ;Elson, 1988) . Those responses are prescribed by mechanical properties of the cell such as stiffness, elasticity, and viscosity.Although many researchers have contributed to the task of characterizing the mechanical properties of cytoplasm (e.g ., Seifriz, 1952;Hiramoto, 1970Hiramoto, , 1976Yoshimoto and Kamiya, 1978;Achenbach and Wohlfarth-Bottermann, 1980;Matsumura et al, 1980;Sato et al ., 1983) no one has yet produced a comprehensive description that considers both the nature of the loads and their time history (Elson, 1988) . As a result, mathematical models of morphogenesis have re-© The Rockefeller University Press, 0021-9525/92/04/83/11 $2 .00 The Journal of Cell Biology, Volume 117, Number 1, April 1992 83-93 membrane, thus allowing control over intracellular milieu .…”

“…Although many researchers have contributed to the task of characterizing the mechanical properties of cytoplasm (e.g ., Seifriz, 1952;Hiramoto, 1970Hiramoto, , 1976Yoshimoto and Kamiya, 1978;Achenbach and Wohlfarth-Bottermann, 1980;Matsumura et al, 1980;Sato et al ., 1983) no one has yet produced a comprehensive description that considers both the nature of the loads and their time history (Elson, 1988) . As a result, mathematical models of morphogenesis have re-membrane, thus allowing control over intracellular milieu .…”

“…The mechanical properties of cytoplasm depend on both the magnitude and the rate of the applied forces (Seifriz, 1952;Ferry, 1980;Sato et al, 1983Sato et al, , 1987 ; and (b) cell properties can vary with the concentrations of different intracellular ions (Ueda et al, 1978; Yoshimoto et al, 1981a,ó ;Pollard and Mooseker, 1981) as well as the concentration of ATP (Matsumura et al, 1980;Ogihara, 1982 Characterization of cytoplasm mechanical properties can also yield information about the ultrastructure ofcytoplasm . By exploring how a material (in this case cytoplasm) reacts to forces such as tension (pulling) or compression (pushing) it is possible to deduce information about the organization of that material (Elson, 1988).…”

A three-dimensional model of cell movement in multicellular systems

“…While this is an important attempt at modeling the motion of the slug, there are limitations to the model. Firstly, it is known that cytoplasm is not a simple Newtonian fluid, as they assume [26,33]. Secondly, the properties of the extracellular fluid, which are critical for the model, are not known.…”