Changes In Cell Geometry Research Articles

Rheology of foaming aluminum melts

Aluminum foam with a closed cellular structure was prepared by a direct foaming method. In the foaming process, the aluminum melt was mechanically agitated, and when a suitable viscosity was achieved, a granular blowing agent was injected. Foam expansion ensued rapidly, and control of the melt viscosity was critical to achieve stable foam without slumping. The rheology of molten aluminum foam was studied as a function of position within the mold cavity and correlated with changes in cell geometry. The deformation pattern of the cell shapes during foam expansion was considered macroscopically and microscopically. Simple mechanical models were introduced to describe the expansion process.

Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

A major development in smooth muscle research in recent years is the recognition that the myofilament lattice of the muscle is malleable. The malleability appears to stem from plastic rearrangement of contractile and cytoskeletal filaments in response to stress and strain exerted on the muscle cell, and it allows the muscle to adapt to a wide range of cell lengths and maintain optimal contractility. Although much is still poorly understood, we have begun to comprehend some of the basic mechanisms underlying the assembly and disassembly of contractile and cytoskeletal filaments in smooth muscle during the process of adaptation to large changes in cell geometry. One factor that likely facilitates the plastic length adaptation is the ability of myosin filaments to form and dissolve at the right place and the right time within the myofilament lattice. It is proposed herein that formation of myosin filaments in vivo is aided by the various filament-stabilizing proteins, such as caldesmon, and that the thick filament length is determined by the dimension of the actin filament lattice. It is still an open question as to how the dimension of the dynamic filament lattice is regulated. In light of the new perspective of malleable myofilament lattice in smooth muscle, the roles of many smooth muscle proteins could be assigned or reassigned in the context of plastic reorganization of the contractile apparatus and cytoskeleton.

MECHANICAL ASPECTS OF CELL SHAPE REGULATION AND SIGNALING

Physical forces play a critical role in cell integrity and development, but little is known how cells convert mechanical signals into biochemical responses. This mini-review examines potential molecular mediators like integrins, focal adhesion proteins, and the cytoskeleton in the context of a complex cell structure. These molecules-when activated by cell binding to the extracellular matrix-associate with the skeletal scaffold via the focal adhesion complex. Vinculin is presented as a mechanical coupling protein that contributes to the integrity of the cytoskeleton and cell shape control, and examples are given of how mechanical signals converge into biochemical responses through force-dependent changes in cell geometry and molecular mechanics.

Complexity in simplicity: monogenic disorders and complex cardiomyopathies.

nents of the primary cardiac cytoarchitecture, including components of the cardiac contractile sarcomere, and the intrasarcomeric, and extrasarcomeric cytoskeleton (2, 3, 7). The cytosol of all eukaryotic cells contains a network of protein filaments and associated proteins which collectively constitute the cytoskeleton. Among these filaments are the actin microfilaments, the somewhat wider tubulin microtubules, and the intermediate filaments. To perform force-generating contraction, and to accommodate the repetitive changes in cell geometry that occur during each cardiac cycle, cardiac myocytes have evolved an abundant and highly specialized cytoskeleton, whose components can be classified into the following 3 groups: (a) The force-generating contractile sarcomeric cytoskeleton consists of a highly-ordered arrangement of myosin thick filaments, actin thin filaments, and associated proteins, such as the troponin‐tropomyosin complex. The repeating sarcomere units are arranged in series, resulting in striated myofibrils. (b) The intrasarcomeric cytoskeleton contains titin, α-actinin, myosin binding protein C, and other proteins that anchor myofilaments and their sarcomeric units and regulate the displacement of myofilaments during each contraction cycle. (c) The extrasarcomeric cytoskeleton is composed of desmin and lamin-containing intermediate filaments that provide a link between adjacent myofibrils and a framework for the nuclear envelope. This extrasarcomeric network also includes subsarcolemmal proteins that provide a connection between the peripheral myofibrils to the sarcolemma and to the extracellular matrix. These include the subsarcolemmal proteins dystrophin and its associated glycoproteins which link the sarcomere to the extracellular

Cell size and geometry of spinal cord motoneurons in the adult cat following the intramuscular injection of adriamycin: comparison with data from aged cats

Adriamycin (ADM), an antineoplastic antibiotic, when injected intramuscularly, is taken up by motoneuron axonal terminals and retrogradely transported to the motoneuron soma where it exerts its neurotoxic effect. In the present study, ADM was injected into the hindlimb muscles of five adult cats. Measurements of the electrophysiological properties of the lumbar motoneurons innervating these muscles were obtained using intracellular recording techniques. Based upon these data the equivalent cylinder model of motoneurons was employed to evaluate ADM-induced changes in cell size and cell geometry. The size of cell somas in the ventral horn was also measured using light microscopy and computer imaging software. There were significant increases in the membrane time constant (25%) and input resistance (50%) in motoneurons whose muscles were treated with ADM (ADM-MNs) compared with data from control motoneurons (control-MNs). The increase in membrane time constant is attributed to an increase in membrane resistance; the increase in input resistance appears to depend upon both an increase in membrane resistance and a decrease in total cell surface area. Cell capacitance, which is proportional to the total cell surface area, was significantly reduced (15%) in ADM-MNs. Calculations based on cable theory indicate that while there was no significant change in the length of the equivalent cylinder for ADM-MNs, there was a significant decrease (17%) in the diameter of the equivalent cylinder. These data indicate that there is a decrease in total cell surface area which can be attributed to the shrinkage of branches throughout the dendritic tree. There was also a small (7%) but statistically significant decrease in the electrotonic length of ADM-MNs. Morphological analysis also revealed that the mean cross-sectional area of the somas of those ventral horn neurons which are likely to correspond to the motoneuron population was significantly reduced on the ADM-treated side compared to that of neurons on the control side. We conclude that significant geometrical changes were induced in lumbar motoneurons of adult cats after ADM was injected into their target muscles. In old cats, spinal cord motoneurons exhibit similar patterns of changes in their electrophysiological characteristics which have also been suggested to be correlated with changes in cell geometry. The question then arises as to whether the response of motoneurons to ADM and the aging process reflects a stereotypic reaction of motoneurons to a variety of insults or whether the response to ADM mirrors specific aspects of the aging process.

Corneal endothelial wound repair in normal and mitotically inhibited cultures.

The aim of the present study was to compare the morphology, proliferative activity and cytoskeletal organization of bovine corneal endothelial cells during wound healing under normal and mitotically inhibited conditions. Cell cultures were grown to confluency and incubated with the mitotic inhibitor 5-fluorouracil (5-FU; 2.5 micrograms/ml) followed by a touch wound. Control cultures were maintained without 5-FU. Mitotic activity, F-actin, vinculin, vimentin and connexin 43 localization were evaluated before, during and after wound closure. 5-FU inhibited irreversibly the mitotic activity of corneal endothelial cells during the whole wound healing process. In the presence of 5-FU, a high degree of polymegathism and delay in actin and vinculin redistribution to the cell borders after wound closure was observed. Vimentin and connexin 43 immunolabeling revealed only slight differences between 5-FU-treated and control cultures. Significant changes in cell geometry and cytoskeletal organization in the amitotic corneal endothelium became manifested only after wounding. These changes may influence cell-cell and cell-matrix interactions as well as functional restoration of the monolayer after wound closure.

Use of Multiple Electrodes To Provide Uniform Potential Distribution during Controlled Potential Electrolysis

In practice, the size of a single working electrode in controlled potential electrolysis cells can be extended in only two dimensions while maintaining uniform potential distribution. A previously published theoretical model predicted that working electrode dimensions in controlled potential electrolysis cells could be effectively extended in three directions while maintaining form potential distribution by using several working electrodes interconnected with appropriately chosen external resistors. A controlled potential electrolysis cell utilizing three working electrodes placed at successively increasing distances along the current path from the counter electrode has been designed and tested. The electrodes were connected in either series or parallel with external compensating resistors calculated according to theory. Nearly identical interfacial potentials were observed for all three electrodes, with dramatic reduction of the potential errors observed without the use of the external resistors. It was further demonstrated that if optimum placement of the reference electrode did not pertain, then the multiple electrode/external resistance network behaved as a single electrode operating with a single uncompensated solution resistance. This should facilitate the use of conventional positive feedback techniques to mimimize potential control errors. Because changes in cell geometry or solution require different sets of compensating resistors, two operational amplifier-based circuits which eliminate this inconvenience were designed and tested. The circuits employ comparison of either individual electrode currents or potentials and feedback control to maintain these at identical value

Regulation of functional cytodifferentiation and histogenesis in mammary epithelial cells: role of the extracellular matrix.

Primary mammary epithelial cells provide a versatile system for the study of hormone and extracellular matrix (ECM) influences on tissue-specific gene expression. We have characterized the formation of alveolarlike morphogenesis and mammary-specific functional differentiation that occur when these cells are cultured on a reconstituted basement membrane (EHS). Cells cultured on EHS exhibit many ultrastructural and biochemical features indicative of polarized and functionally differentiated mammary epithelium in vivo. The increased expression and specific vectorial secretion of milk proteins into lumina formed in culture are accompanied by large increases in milk protein mRNA expression. However, when individual ECM components are tested, smaller increases in milk protein mRNA are measured on heparan sulfate proteoglycan (HSPG) and laminin, and these responses are not associated with full functional cytodifferentiation or histotypic configuration. This indicates that multiple levels of regulation are involved in mammary-specific gene expression, and that in addition to individual ligand requirements cooperative interactions between various ECM molecules and cells are necessary for functional differentiation in culture. We have also shown that endogenous production of ECM molecules and changes in cell geometry are correlated with changes in functional and histogenic gene expression. We have previously proposed a model of cell-ECM interactions that is consistent with these data.

Mucociliary transport and epithelial morphology with elongation and collapse in rat trachea.

Mucociliary clearance in the trachea depends on a close relationship between structure and function of the components of its mucociliary system. Current explanations of normal mucociliary function denote narrow tolerances to change in factors such as the depth of secretions lining the lumen and the distribution of cilia. This study centered on changes in airway length under physiological conditions in the rat. Following extension of the head, the length of the trachea increased 50% without change in diameter. The rate of mucociliary clearance did not change with head position, averaging 3.79 +/- 1.03 mm/min in the flexed and 3.81 +/- 1.10 mm/min in the extended position. Extension of the head caused surface epithelial cells to elongate longitudinally and to decrease in height. These changes were greater in ciliated cells than in mucus-containing cells, thus accentuating the degree of protrusion of the secretory cells into the lumen of the stretched trachea. It is proposed that, during head extension, the relative protrusion of secretory cells into the lumen added bulk to the volume otherwise occupied by luminal secretions, and that these consistent changes in cell geometry served to adjust the height of ciliary tips within the periciliary fluid, thus mitigating fluctuations in the depth of the fluid. It was concluded that the mucociliary system of tracheas subjected to substantial change in configuration supported clearance because spatial relationships of essence to mucociliary function were maintained.

Physiological characterization of adaptive clones in evolving populations of the yeast, Saccharomyces cerevisiae.

Populations of a diploid strain of S. cerevisiae were grown in glucose-limited continuous culture for more than 260 generations. A series of seven sequential adaptive changes were identified by monitoring the frequency of cycloheximide resistance in these populations. Samples were taken from the continuous cultures following each adaptive shift and characterized physiologically to determine (1) the range of phenotypes that can be selected in a precisely defined constant environment and (2) the order and predictability of the occurrence of the adaptive mutations in evolving populations. The clones were characterized with respect to the growth parameters, maximum growth rate, saturation coefficient and yield, as well as for changes in cell size and geometry and rate of glucose uptake. The maximum growth rates of the seven adaptive clones were very similar, but in contrast the saturation coefficients differed substantially. Surprisingly, not all clones showed reductions in the saturation coefficients, in comparison to the immediately preceding clones, as would be predicted from classical continuous culture kinetics. In addition, yield estimates first increased and then decreased for later isolated adaptive clones. In general, the results suggest epistatic interactions between the adaptive clones, consistent with earlier published results. The rate of glucose uptake, as measured by 14C-xylose uptake, increased dramatically after the selection and fixation of seven adaptive clones. Progressive decreases in cell volume and changes in cell geometry, resulting in increased surface area to volume ratios, were also observed in the adaptive clones, but these changes were not always seen in other haploid and diploid yeast populations evolving under the same conditions. Such changes may be easily explainable in terms of the characteristics of the glucose-limited environment. The significance of the results to the evolution of microorganisms under nutrient-limiting conditions is discussed.

Progress in industrial demonstration of advanced unipolar electrolysis

Abstract Continuing development of industrial unipolar electrolysers has led to two generations of advanced designs. The Generation I design is based on modifications to proved commercial equipment, with use of electrode activation techniques to achieve significant reductions in operating voltages at increased current levels. The Generation II design incorporates changes in cell geometry which significantly reduce the ohmic resistance and allow economic operation at current densities above 5 kA m−2. Construction has recently been completed of a 1.2-MW experimental plant which is being used for evaluation of full-scale commercial modules of the new electrolyser designs. This facility is described, and initial performance results from the first 600-kW phase of Generation I cells are reported. This report is supported by data from 12 000 h of operation of 20-kW prototype cells, and from testing of electrode activation systems in 2-kW pilot electrolysers.

The Effect of Changes in Cell Geometry Associated with Freezing on the Radiation Dose from Decay of Internal Isotopes

(1982). The Effect of Changes in Cell Geometry Associated with Freezing on the Radiation Dose from Decay of Internal Isotopes. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 41, No. 1, pp. 99-103.

Alteration of the erythrocyte ultrastructure and blood viscosity by morphine.

The effects of acute morphine administration on intact erythrocytes and on their flow properties were studied by measuring the mean cell volume, cell geometry, and whole blood and plasma viscosities. Morphine caused a small (2-7%) increase in mean cell volume. Changes in cell geometry were found to be time dependent and most pronounced in concave portions of the red cells. Whole body viscosity was found to decrease upon morphine treatment; this may be due in part to a concurrent decrease in plasma viscosity.