Gradients chemotactic

Previous studies indicate that osmotic gradients promote membrane fusion, while hyperosmotic conditions inhibit membrane fusion during exocytosis. Consistent with this idea is the observation that the release of lysosomal enzymes from rabbit neutrophils, induced by the chemotactic peptide J -formylmethionyl-leucyl-phenylalanine (FMLP), is inhibited almost 80% in a 700-mosmol/kg medium. Inhibition is immediate (within 10 s), increases with osmolality, and is independent of the osmoticant. Neutrophils loaded with the calcium indicator indo-1 exhibit an FMLP-induced calcium signal that is inhibited by hyperosmolality. Hyperosmolality (700 mosmol/kg) increases basal calcium levels and reduces the peak of the calcium signal elicited by FMLP at concentrations ranging from 10 ° to 10 M. 

Neutrophils may move at speeds of up to 20 /tm min-1 in response to chemoattractants such as denatured proteins, lipids, peptides or C5a. Movement may be defined either as chemokinesis, which is generalised (non-directional) locomotive activity, or as chemotaxis, which is orientation and directional migration up a concentration gradient. A concentration difference at opposite ends of the cell of only 1% is sufficient to activate such directional movement. However, neutrophils do not respond chemotactical-ly to static gradients of chemoattractants, and both temporal and directional changes in chemoattractant concentrations are required. 

Once inflammatory cells have infiltrated into the tissue, they respond to chemotactic gradients established by cytokines and chemokines, which origin from sites of injury or infection. These... 

Macrophage release of chemotactic factors also attracts fibroblasts, an effect that has been studied in animals and humans. The factors are sufficiently strong and specific that fibroblasts migrate up a concentration gradient (tested in artificial chambers) and can induce replication (in vivo experiments). Thus, fibroblasts—the primary source of structural proteins, notably collagen— can be mobilized by AM to the inflammatory sites and can also markedly increase in number in response to secretion of activated AMs. These factors, in addition to the other activities and secretions of the AM, are being characterized (Gee, 1984). 

Defined chemotactic gradients, direct ceU chemotaxis visualization by microscope (also time-lapse)... 

Zigmond SH (1977) Ability of polyrnorpho-nuclear leukocytes to orient in gradients of chemotactic factors. J Cell Biol 75 606-616... 

Standard models for bacterial chemotaxis are based on the behavior of nonmarine enteric bacteria.196 Chemotactic behavior of nonmarine bacteria consists of discrete steps of short runs interspersed with tumbling, resulting in the random repositioning of the cells, i.e., the classical random walk. As a consequence, the net speed up a chemical gradient via the random-walk response is only a few percent of the swimming speed. The relatively slow speed and mode of chemotaxis displayed by nonmarine enteric bacteria would restrict the ability of marine bacteria to respond to chemical gradients in the sea and hence cast doubt on the importance of chemotaxis for bacteria in turbulent marine environments. 

A methylesterase which catalyzes the hydrolysis of y-glu-tamyl methyl esters of membrane bound proteins in Salmonella typhimurium and JJ. coli has recently been identified (25). Apparently, these membrane-bound proteins undergo methylation by a S-adenosylmethionine requiring methyltransferase (similar to transferase II). In this case the methylation and demethylation are directly associated with the chemotactic mobility of the microorganisms. When the cells are exposed to a chemotactic attractant, methylation of the membrane-bound proteins increases and straight-line movement up the gradient is induced. When the attractant is removed or a repellent substituted, the esterase decreases the methylation and random movement results. These control mechanisms are analogous in regulation to some of the reversible processes such as adenylation (26), uridylation (27) and phosphorylation (28). 

Under agarose. This assay was originally developed to study leukocyte migration (Nelson et al., 1975) however, it has also been applied to the study of chemotactic and chemokinetic effects of FGF on endothelial cells (Stokes et al., 1990). Cells are allowed to migrate under an agarose gel in which a chemoattractant (or a control solution) forms a diffusion gradient. The differential migration of cells toward the chemoattractant is taken as a measure of its chemotactic activity. 

Chemotaxis (chemotactic) the process by which motile organisms migrate to and accumulate in a part of a chemical gradient. 

Leukocyte slides along the chemotactic gradient of CKs sequestered on the endothelium. 

Leukocyte migrates to the tissues, guided by tissular chemotactic gradients. 

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