A polarization model overcoming the geometric restrictions of the laplace solution for spheroidal cells: obtaining new equations for field-induced forces and transmembrane potential.
(9/842)
We present a new model for a variety of electric polarization effects on oblate and prolate homogeneous and single-shell spheroids. For homogeneous spheroids the model is identical to the Laplace model. For single-shell spheres of cell-like geometry the calculated difference of the induced dipole moments is in the thousandths range. To solve Laplace's equation for nonspherical single-shell objects it is necessary to assume a confocal shell, which results in different cell membrane properties in the pole and equator regions, respectively. Our alternative model addresses this drawback. It assumes that the disturbance of the external field due to polarization may project into the medium to a characteristic distance, the influential radius. This parameter is related to the axis ratio of the spheroid over the depolarizing factors and allows us to determine the geometry for a finite resistor-capacitor model. From this model the potential at the spheroid's surface is obtained and, consequently, the local field inside a homogeneous spheroid is determined. In the single-shell case, this is the effective local field of an equivalent homogeneous spheroid. Finally, integration over the volume yields the frequency-dependent induced dipole moment. The resistor-capacitor approach allowed us to find simple equations for the critical and characteristic frequencies, force plateaus and peak heights of deformation, dielectrophoresis and electrorotation for homogeneous and single-shell spheroids, and a more generalized equation for the induced transmembrane potential of spheroidal cells. (+info)
The structure and function of folliculo-stellate cells in the anterior pituitary gland.
(10/842)
The folliculo-stellate cells (FS cells) in the anterior pituitary gland are characterized by their star-like appearance and their ability to form follicles. Although FS cells do not produce any pituitary hormones, their special tendency to surrounding endocrine cells with their long cytoplasmic processes suggests that they regulate endocrine cells by intercellular communication. In spite of many morphological and cytophysiological studies recently performed, a precise understanding of the major functions of FS cells in the pituitary gland remains obscure. We review here the morphological characteristics of FS cells and their suspected functions in the anterior pituitary gland. It is well established that the FS cell produces many kinds of growth factors, i.e., fibroblast growth factor, vascular endothelial cell growth factor and interleukin 6. The biological significances of these growth factors in the anterior pituitary gland are also discussed in this paper. The origin and differentiation of FS cells, especially the possibility that the FS cell is a kind of stem cell which has the potential to differentiate into endocrine cells, is also presented. (+info)
Mathematical simulation and analysis of cellular metabolism and regulation.
(11/842)
MOTIVATION: A better understanding of the biological phenomena observed in cells requires the creation and analysis of mathematical models of cellular metabolism and physiology. The formulation and study of such models must also be simplified as far as possible to cope with the increasing complexity demanded and exponential accumulation of the metabolic reconstructions computed from sequenced genomes. RESULTS: A mathematical simulation workbench, DBsolve, has been developed to simplify the derivation and analysis of mathematical models. It combines: (i) derivation of large-scale mathematical models from metabolic reconstructions and other data sources; (ii) solving and parameter continuation of non-linear algebraic equations (NAEs), including metabolic control analysis; (iii) solving the non-linear stiff systems of ordinary differential equations (ODEs); (iv) bifurcation analysis of ODEs; (v) parameter fitting to experimental data or functional criteria based on constrained optimization. The workbench has been successfully used for dynamic metabolic modeling of some typical biochemical networks (Dolgacheva et al., Biochemistry (Moscow), 6, 1063-1068, 1996; Goldstein and Goryanin, Mol. Biol. (Moscow), 30, 976-983, 1996), including microbial glycolytic pathways, signal transduction pathways and receptor-ligand interactions. AVAILABILITY: DBsolve 5. 00 is freely available from http://websites.ntl.com/ approximately igor.goryanin. CONTACT: [email protected] (+info)
The malonyl-CoA-long-chain acyl-CoA axis in the maintenance of mammalian cell function.
(12/842)
Long-chain acyl-CoA esters have potent specific actions (e.g. on gene transcription, membrane trafficking) as well as non-specific ones (e.g. on phospholipid bilayers). They are synthesized on the cytosolic aspects of several intracellular membranes, to give rise to (a) cytosolic pool(s) to which a variety of enzymes and processes have access, including some localized in the nucleus. Their concentration in cells is highly regulated, interconversion with corresponding acylcarnitines being the most important mechanism involved. This reaction is catalysed by cytosol-accessible carnitine long-chain acyl (palmitoyl) transferase activities that are themselves located on multiple membrane systems. Regulation of these activities is through the inhibitory action of malonyl-CoA. Hence the existence of a potent malonyl-CoA-acyl-CoA axis through which many processes involved in the maintenance of mammalian cell function are regulated. The molecular, topographical and physiological interactions that make this possible are described and discussed. (+info)
New microscope gives scientists the inside scoop on living cells.
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Scientists at Pacific Northwest National Laboratory in Richland, Washington, have developed a unique imaging system capable of focusing on a single living cell within an organism. This new technology will be used in what the multidisciplinary team has termed a "cellular observatory" to study the effect of environmental insults to live cells. (+info)
Developmental and cell biological functions of the Drosophila DEAD-box protein abstrakt.
(14/842)
BACKGROUND: DEAD-box proteins are a large family of proteins found in bacteria, plants and animals, but only few have been analysed functionally. They are involved in the regulation of various aspects of RNA processing and metabolism, including splicing, transport and translation. The study of their function in multicellular organisms has been restricted to a few special cases, such as the Vasa protein in the fruit fly Drosophila. RESULTS: We show that abstrakt, a gene originally identified genetically by its effect on axon outgrowth and fasciculation of the Bolwig nerve, encodes a new Drosophila DEAD-box protein of which the closest homologue is a human gene of unknown function. Using temperature-sensitive alleles to assay its function, we found that abstrakt is essential for survival at all stages throughout the life cycle of the fly. Mutants show specific defects in many developmental processes, including cell-shape changes, localisation of RNA and apoptosis. CONCLUSIONS: Abstrakt is not globally required for RNA splicing, transport, subcellular localisation or translation. Nevertheless, there is a widespread requirement for Abstrakt during post-transcriptional gene expression. Abstrakt must affect processing of specific subsets of RNAs, suggesting that differential post-translational control during development is more common than previously suspected. (+info)
A simple, inexpensive method for teaching how membrane potentials are generated.
(15/842)
We have developed a simple laboratory exercise that uses an inexpensive dialysis membrane (molecular weight cutoff = 100) to illustrate the generation of membrane potentials (Vm) across plasma membranes of animal cells. A piece of membrane approximately 2.0 cm2 is mounted in an Ussing-like chamber. One chamber half is designated cytosol and the other half external. Chamber sidedness helps students relate their findings to those of real cells. As in real cells, outward directed K+ concentration gradients [high cytosolic K+ concentration ([K+]c) and low extracellular K+ concentration] generate cytosol electrically negative Vm with a slope of approximately -45 mV/decade change in [K+]c. The polarity of Vm reflects the outward flow of potassium ions because flow of the larger counterion, H2PO4-, is restricted to the pores in the membrane. A slope less than Nernstian (<59 mV/decade) suggests that the membrane is slightly permeable to H2PO4-. Importantly, this facilitates teaching the use of the Nernst equation to quantify the relationship between ion concentration ratios across membranes and magnitude of Vm. For example, students use their data and calculate a permeability ratio PK/PH2PO4 that corresponds to a slope of approximately 24% less than Nernstian. This calculation shows that Nernstian slopes are achieved only when permeability to the counterion is zero. Finally, students use the concept of membrane capacitance to calculate the number of ions that cross the membrane. They learn where these ions are located and why the bulk solutions conform to the principle of electroneutrality. (+info)
Section 5--nonthermal bioeffects in the absence of well-defined gas bodies.
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The purpose of this section is to describe bioeffects that occur in those instances in which gas bodies are not known to commonly be present. This is in contrast to situations such as lung and intestine, where bioeffects have been proposed to be associated with the known presence of gas (Section 4). In addition, this section does not include those studies in which microbubbles (such as ultrasound contrast agents) are purposefully introduced (Section 6). Therefore, this section includes a large collection of bioeffects that may be related to cavitation activity or may not be related at all to the presence of gas bodies. The intention is to provide an overall summary of the information currently available that pertains to those situations in which gas bodies are not known to be present and to provide this information in support of conclusions and recommendations on this subject. (+info)