Effects Of Chemoattractants Research Articles

Chemoattractants: Their essentiality and efficacy in shrimp aquaculture

Aquaculture serves as a sustainable source of good quality wholesome food and major input is feed. In recent years, considerable quantities of plant sources have been attempted for inclusion in shrimp feed, due to high demand and high cost of fishmeal. Plant-based ingredients are in general poor in attractability and palatability to aquatic species compared to marine sources. It is desirable to develop an economical and nutritious feed that is attractive and palatable for ensuring reduction of feed wastage. Chemoattractants nowadays are unavoidable in commercial shrimp feeds and are included either individually or in combination. The present review revealed that the various marine sources, in particular krill meal would be more effective for aquatic species, compared to those derived from vegetable origin and chemical compounds. In addition to acting as a feed attractant, marine sources serve as a potential fishmeal substitute due to their rich nutritional composition. However, certain biogenic amines present in these marine-based ingredients need to be examined before their use, since these amines when present in high concentrations reduces feed intake by producing undesirable odour. Use of a combination of chemoattractants would give a better effect, rather than using them individually and compounds from plant origin have limited beneficial effects. The present review concludes that incorporation of chemoattractants would be beneficial in formulation of enriched and economical feeds with better attractability and palatability. The selection of suitable attractant and their supplementation at correct proportion is significantly more important to avoid undesirable effects in cultured shrimp. Further field-based research is needed to predict the actual effects of chemoattractants on farmed shrimp and to provide a sustainable base for the expansion of shrimp aquaculture sector, by reducing feed wastage.

Abstract 3103: Analysis of breast cancer lines and PDXs using a blood brain niche (µm-BBN) microfluidic device and algorithms to aid diagnosis of brain metastatic potential

Abstract Metastasis from the primary tumor site to the brain is the most lethal complication of advanced breast cancer. There is no translational approach to detect if a primary tumor has brain metastatic potential. This is due to a lack of blood brain barrier (BBB) models that can classify a cells metastatic potential. Moreover, the mechanisms by which circulating cancer cells extravasate through the BBB are unknown. Currently used in vivo murine models are slow to manifest metastasis therefore, an alternative approach is an in vitro microfluidic model that re-capitulates the BBB niche micro-environment. Our goal is to develop and use this model to identify the metastatic potential of cancer cell populations. Therefore, we have developed a blood brain niche (µm-BBN) on-a-chip and studied the phenotypic differences between cancer cells in the µm-BBN. The device has two chambers separated by a 5µm porous membrane coated with Matrigel and a BB human endothelial cell (hCMEC/D3) mono-layer. The bottom chamber contains a brain stromal ECM and Normal Human Astrocytes (NHA), while the top chamber acts as the blood vessel. Cancer cells are introduced into the top chamber and allowed to extravasate into the brain like stroma. We measured the ability of the endothelial layer to prevent fluorescent small molecules from diffusing into the brain stromal space. The barrier measured 8.3X lower max fluorescent values than when no barrier was present and were confirmed by TEER. Using this model, we characterized the MDA-231 breast cancer cell line against a brain-seeking subclone (MDA-231-BR), normal-like cell lines (MCF10A) and brain met patient derived xenografts (PDXs) in terms of their ability to extravasate, migrate and survive in the niche for 24-48 hrs. Phenotypic and migratory behavior was recorded using confocal tomography to measure cancer cell properties (volume, shape, position) relative to the endothelial layer. Brain-seeking subclones cluster around the endothelial layer, the MCF10A cell line has no preferred location and the parent line (MDA-231) extravasates deeper into the brain stromal space than the other two cell lines. We also found significant variation in the shape of each cell line before and during extravasation suggesting differences in plasticity. The effects of chemoattractants within the µm-BBN on extravasation have been explored by omitting astrocytes in the collagen-infused brain niche and replacing with astrocyte conditioned media. These findings confirm that the system is capable of measuring both variations in cancer cell populations and individual cells. This approach may enable classification of subclone populations with higher metastatic potential, meeting a major need in Oncology. Future work will employ this emerging tool to study the mechanisms by which the cancer cells extravasate and survive in the niche. Citation Format: Christopher Ryan Oliver, Megan Altemus, Trisha Westerhof, Aki Morikawa, Xu Cheng, Jason Heth, Shuichi Takayama, Maria Castro, Sofia Merajver. Analysis of breast cancer lines and PDXs using a blood brain niche (µm-BBN) microfluidic device and algorithms to aid diagnosis of brain metastatic potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3103.

The role of BMP-2, low-level laser therapy and low x-ray doses in dental follicle stem cell migration

ABSTRACTThe knowledge of how cells respond to different treatments in terms of their migration potential could improve bone regeneration and osseointegration of dental implants. The objective of this study was to elucidate the effects of various chemoattractants, bone morphogenetic protein-2 (BMP-2), low-level laser therapy (LLLT), and cone beam computed tomography (CBCT) on the migration of dental follicle stem cells (DFSCs). The chemoattractants used in our study were the serum-free (SF) conditioned media that were harvested from osteoblast cell cultures seeded on the surface of titanium implants—Ti6Al7Nb (TiCtrl), implants infiltrated with hydroxyapatite (TiHA), with silicatitanate (TiSiO2), and from culture of DFSCs cultivated on TiCtrl implants. We used the scratch migration assay to evaluate the influence of BMP-2, LLLT therapy, and CBCT on the migration potential of DFSCs. The migration scratch assay indicates that the BMP-2 growth factor is able to increase the DFSC migration compared to control culturing medium and regardless of laser or CBCT exposure. The results demonstrate the importance of improving the implant surface with HA, SiO2, and DFSCs. Stimulated DFSCs will secrete growth factors which will act as chemoattractants for the stem cells of the implant host. Adding growth factors such as BMP-2 can improve the migration process of DFSCs.

Differential effects of chemoattractants on mast cell recruitment in vivo

Rats were injected with rat recombinant (rr) IL3, rrSCF, rrIL-3+rrSCF, rrRANTES and LTB4. Six hours after subcutaneous injection of rrIL-3 or rrIL-3+rrSCF, there was an increase in mast cell numbers in the skin and spleen. Peritoneal mast cells were recruited following i.p. injection of rrIL-3, but with rrIL-3+rrSCF recruitment was delayed. Immunostaining with a mast cell specific antibody showed that immature orthochromatic mast cells were being recruited. rrIL-3 induced recruitment of mast cells to the peritoneal cavity was blocked by anti-integrin antibodies. Mast cell recruitment depended on the target tissue and the time of exposure to the chemoattractant.

Fundamental study of osteoclast chemotaxis toward chemoattractants expressed in periodontitis

Periodontitis is a chronic inflammatory disease that leads to bone resorption by osteoclasts (OCs). Several factors contribute to the differentiation of OCs from hematopoietic precursors. Cellular chemotactic factors are expressed in periodontitis tissue, but the effects of these chemoattractants on OCs are not well understood. Here we examined the effects of chemoattractants produced in inflamed periodontal tissue on OC chemotaxis. Rat bone-marrow OCs were cultured in OC culture medium for 3 or 6d. Using EZ-TAXIScan™, the chemotactic response of these OCs to several chemoattractants [monocyte chemotactic protein-1; macrophage inflammatory protein 1α; regulated on activation, normal T-cell expressed and secreted; stromal cell-derived factor-1α; and complement activation product 5a (C5a)] was measured. In addition, we measured the effect of C5a-specific inhibitors on chemotactic responses toward C5a. The recorded chemotactic responses were quantitatively analysed using ImageJ software. Chemoattractants associated with periodontal disease significantly increased the chemotactic activity of differentiated rat OCs in a concentration-dependent manner, with C5a inducing the highest chemotactic activity of OCs cultured for 3 or 6d. The C5a-specific inhibitor significantly inhibited chemotaxis toward C5a in a concentration-dependent manner. We suggest that C5a plays an important role in pathologic bone resorption in periodontal disease by stimulating the chemotaxis of OCs. Therefore, C5a is a potential target for the treatment of periodontal disease.

Abstract 2370: Single cell analysis using a microscale migration slide

Abstract Cell migration occurs in a variety of biological processes including wound healing, embryonic development, and immune responses. Existing chemotaxis assays used to assess cell migration employ the Boyden chamber which lack real-time imaging capability and does not maintain well defined biomolecular gradients. To overcome these limitations, a cell migration assay was developed which enabled real-time monitoring of single cells on a slide-like platform that maintained a stable linear gradient. Fluorescence measurements with albumin (MW=66kDa) conjugated with FITC demonstrated that the concentration profile was linear over the 1 mm observation area. This linear concentration gradient was established after 1 hour incubation and was stable for over 24 hours. The microscale migration slide was used to assess the effects of serum concentrations (0, 2, 5, 10, and 15%) on the migration propensity of four different cell lines that were grown on collagen. The cell lines included cancer cell lines with known invasive properties (fibrosarcoma cancer cells HT1080 and breast cancer cells MDA-MB-231), along with HUVECs which are angiogenic cells involved in tumor metastasis and a control cell line, NIH 3T3 fibroblast cells. Cells were incubated in the experimental conditions overnight (12 hours) with images captured every 15 minutes. Migration of single cells was monitored and imaged in real-time and the percentage of cells that exhibited positive migration towards the chemotactic source was calculated. Interestingly, we observed that the highest percentage of migratory HUVEC cells was obtained using 2% serum whereas the other three cell lines exhibited increased migration with increasing serum concentration. Under similar culture conditions of either 10 or 15% serum, MDA-MB-231 possessed the highest migration index, followed by NIH 3T3 fibroblasts and HT1080 cells whereas HUVEC cells did not migrate at all under these high serum conditions. Extensive testing over a range of conditions with different users indicated remarkable consistency in the data generated and suggests that the migration slide is a useful tool to monitor the effects of chemoattractants on adherent cell lines. Overall the results provide a reference point from which to build upon future studies aimed at comparing the effects of signaling molecules and growth factors on the migration propensities of cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2370. doi:10.1158/1538-7445.AM2011-2370

Chemo-accumulation without changes in membrane potential in the microstome form of the ciliate Tetrahymena vorax

The swimming behaviour of ciliates is mainly determined by membrane potential and transmembrane fluxes. In a chemical gradient, swimming ciliates may approach or move away from the source. Based on experiments on Paramecium, it is generally assumed that chemical attractants and repellents affect the swimming behaviour of ciliates by specific changes in the membrane potential. We have examined whether there is a causal relationship between membrane potential and chemo-accumulation in the microstome form of the polymorphic ciliate Tetrahymena vorax. Effects of chemo-attractants on the membrane potential of Tetrahymena have not been previously reported. Microstome T. vorax cells aggregated close to a point source of l-cysteine and the complex meat hydrolysate proteose peptone. Chemo-accumulated cells displayed a significantly higher turning frequency than control cells at a similar cell density. A concentration of 20 mmol l(-1) l-cysteine did not evoke any detectable change in the membrane potential whereas 1% proteose peptone depolarised the cells by ∼12 mV. This is contrary to the current model, which predicts agents that induce a moderate depolarisation to be repellents. A solution of 1% proteose peptone contains 21 mmol(-1) Na(+). A solution of 21 mmol(-1) NaCl without organic compounds also caused ∼12 mV depolarisation but had no aggregating effect on the cells. Collectively, the electrophysiological and behavioural data indicate that chemo-accumulation in the microstome form of T. vorax is not governed obligatorily by the membrane potential. We thus suggest that the simple membrane potential model for chemokinesis in Paramecium may not be valid for T. vorax.

How a Cell Crawls and the Role of Cortical Myosin II

The movements of Dictyostelium discoideum amoebae translocating on a glass surface in the absence of chemoattractant have been reconstructed at 5-second intervals and motion analyzed by employing 3D-DIAS software. A morphometric analysis of pseudopods, the main cell body, and the uropod provides a comprehensive description of the basic motile behavior of a cell in four dimensions (4D), resulting in a list of 18 characteristics. A similar analysis of the myosin II phosphorylation mutant 3XASP reveals a role for the cortical localization of myosin II in the suppression of lateral pseudopods, formation of the uropod, cytoplasmic distribution of cytoplasm in the main cell body, and efficient motility. The results of the morphometric analysis suggest that pseudopods, the main cell body, and the uropod represent three motility compartments that are coordinated for efficient translocation. It provides a contextual framework for interpreting the effects of mutations, inhibitors, and chemoattractants on the basic motile behavior of D. discoideum. The generality of the characteristics of the basic motile behavior of D. discoideum must now be tested by similar 4D analyses of the motility of amoeboid cells of higher eukaryotic cells, in particular human polymorphonuclear leukocytes.

5-Oxo-6,8,11,14-eicosatetraenoic Acid Stimulates the Release of the Eosinophil Survival Factor Granulocyte/Macrophage Colony-stimulating Factor from Monocytes

Allergic diseases such as asthma are characterized by tissue eosinophilia induced by the combined effects of chemoattractants and cytokines. Lipid mediators are a major class of endogenous chemoattractants, among which 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is the most potent for human eosinophils. In this study, we investigated the effects of 5-oxo-ETE on eosinophil survival by flow cytometry. We found that this compound could promote eosinophil survival in the presence of small numbers of contaminating monocytes, but not in their absence. The conditioned medium from monocytes treated for 24 h with 5-oxo-ETE also strongly promoted eosinophil survival, whereas the medium from vehicle-treated monocytes had no effect. An antibody against the granulocyte/macrophage colony-stimulating factor (GM-CSF) completely blocked the response of eosinophils to the conditioned medium from 5-oxo-ETE-treated monocytes, whereas an antibody against interleukin-5 had no effect. Furthermore, 5-oxo-ETE stimulated the release of GM-CSF from cultured monocytes in amounts compatible with eosinophil survival activity, with a maximal effect being observed after 24 h. This effect was concentration-dependent and could be observed at concentrations in the picomolar range. 5-Oxo-ETE and leukotriene B(4) had similar effects on GM-CSF release at low concentrations, but 5-oxo-ETE induced a much stronger response at concentrations of 10 nm or higher. This is the first report that 5-oxo-ETE can induce the release of any cytokine, suggesting that it could be an important mediator in allergic and other inflammatory diseases due both to its chemoattractant properties and to its potent effects on the synthesis of the survival factor GM-CSF.

Fertilization success and the effects of sperm chemoattractants on effective egg size in marine invertebrates

The effects of sperm chemoattractants released from eggs of the solitary ascidian Ciona intestinalis were estimated using a molecular-diffusion model. The diffusion coefficient of the chemoattractant was estimated to be between 0.933×10 -5 cm 2 s -1 and 0.124×10 -5 cm 2 s -1 ; the release rate of the chemoattractant from the egg was estimated at 10.6 pg s -1 , and the chemoattractant threshold concentration required to elicit sperm motility was estimated at between 91.3 mg ml -1 and 9.31 mg ml - Our results show that sperm chemoattractants diffuse rapidly from the 170-μm-diameter egg to create an effective egg size (the distance at which free-swimming sperm detect, and are attracted to, the egg membrane) of 2 mm diameter. If even half of the sperm encountering this chemoattractant halo subsequently reach the egg membrane, fertilization success will increase more than 50-fold. This difference is substantial in comparison to the changes in fertilization success, which accrue from changes in physical egg size. We suggest that current theory linking the evolution of marine-invertebrate egg size with fertilization success should be considered with caution until the effects of chemoattractant compounds on fertilization success are better understood.

Cell Migration/Chemotaxis: Biphasic Dose Responses

The dose-dependent effects of chemoattractants on target cell migration such as tumor cells, fibroblasts, and especially neutrophils were assessed. In general, the dose-response characteristics were strikingly biphasic in nature and were independent of both the target tissue and chemoattractant agent. The assessment included evaluations of the quantitative features of the dose-response relationship, mechanistic foundations of the biphasic responsiveness and clinical applications.

Effects of Cytokine-Induced Neutrophil Chemoattractants (CINCs) on Shape Change, Adhesiveness and Phagocytosis of Rat Neutrophils.

Rat cytokine-induced neutrophil chemoattractants (CINC)-1, -2 alpha, -2 beta and -3 belong to alpha-chemokines and are known to be potent chemoattractants for rat neutrophils in vivo and in vitro. In this study, the abilities of CINCs to affect several functions of rat neutrophils are estimated. All CINCs at a concentration of 10(-8) M induced the polarization of rat neutrophils. The adhesion of each CINC-treated neutrophil to fibrinogen significantly increased, reaching a maximal adhesion at 10(-8) M of each CINC. The CINCs enhanced the phagocytosis of heat-killed yeast cells by neutrophils in a dose-dependent manner. In contrast, CINCs did not induce the production of reactive nitrogen intermediates. The results suggest that CINCs play a significant role in neutrophil infiltration and phagocytosis at inflammatory sites in rats.

INFECTIOUS GASTROENTEROCOLITIDES IN CHILDREN: An Update on Emerging Pathogens

The recognition that bacterial infections induce signal transduction responses in infected epithelial cells also provides new avenues to consider as novel forms of therapy. For example, the chemokine interleukin-8, which attracts neutrophils to sites of mucosal infection, is produced by epithelial cells of gastric and intestinal origin in response to bacterial infection. Inhibitors of chemokine production or inhibition of the biologic effects of neutrophil chemoattractants have the potential to reduce both mucosal inflammatory responses and the attendant clinical sequelae. Eukaryotic cells also respond to infection with elevations in cytosolic second messengers, including inositol triphosphate (IP3) and calcium ([Ca2+]i). In intestinal epithelium, these second messengers can mediate the diarrheal response to infection. Calcium/calmodulin inhibitors may have a beneficial effect in treating those gastrointestinal infections mediated through changes in the level of cytosolic free calcium. DuPont and colleagues showed, for example, that oral therapy with zaldaride maleate relieves symptoms of disease and shortens the duration of diarrhea in travelers with ETEC-induced diarrhea. Evaluation of additional signal transduction responses to microbial infections should provide both new insights into the pathogenesis of gastrointestinal infectious diseases and novel approaches to consider for the prevention and therapy for these human illnesses.

Interactions between IL-4, anti-CD40, and anti-immunoglobulin as activators of locomotion of human B cells.

Abstract The locomotor properties of small, surface IgM+ and surface IgD+ B cells from the human tonsil were studied using polarization assays and collagen gel invasion assays. These cells gave poor locomotor responses when freshly isolated from the tonsil; but 30 to 40% of the cells polarized and invaded collagen gels after overnight culture in IL-4 or anti-CD40. IL-13 had a similar but weaker effect. Culture with anti-CD40 and IL-4 together gave a higher proportion of polarized cells than either alone, and culture in anti-CD40, IL-4, and anti-IgM gave a still higher proportion (> 60% of B cells polarized). Polarization increased gradually, during hours of culture, unlike the typical rapid response to chemoattractants. We also studied the immediate (< 30 min) effects of chemoattractants on B cell polarization. B cells cultured overnight then washed, but not B cells fresh from the tonsil, polarized immediately in response to anti-CD40. Similar responses to anti-IgM and anti-IgD, both pre- and postculture were also observed, but the response of cultured cells was stronger. IL-4-cultured B cells invaded collagen gels incorporating anti-IgM, anti-IgD, or anti-CD40 in higher numbers than control gels. Most of the invading cells were surface IgM+. These results suggest that locomotor activation in B cells requires two steps. The capacity for locomotion is growth-related and is first activated by IL-4 or by anti-CD40, enhanced by the presence of anti-IgM. Following activation, the cells respond rapidly to chemoattractants such as anti-Ig or anti-CD40.

Polarization assay studies of human neutrophil motility.

AbstractThe polarization assay was used to assess the effects of chemoattractants on neutrophil motility by means of cellular configuration. The addition of N‐formyl‐L‐methionyl‐phenylalanine (f‐Met‐Phe) to a neutrophil suspension from human peripheral blood induced a polarized change in cellular configuration, and the ratio of such transfiguration reached a maximum at 10–8 to 10–6 M of f‐Met‐Phe. The polarized configuration appeared 1 min after addition of f‐Met‐Phe and showed its maximum response at 10 min. The number of polarized cells were decreased after exposure to cytochalasin B or incubating with corticosteroid. The increased response of random polarization was induced in a dose‐dependent fashion by ascorbic acid. Tetracycline HCl did not cause any changes in cell shape at any concentrations examined. This assay can be used to examine patients with depressed neutrophil motility, such as those with systemic lupus erythematosus in the active phase and a severe case of atopic dermatitis.

Cyclic AMP stimulates accumulation of inositol trisphosphate in Dictyostelium.

Previous studies indicated that in Dictyostelium amoebae signal transmission from cell surface cyclic AMP receptors to intracellular events concerned with chemotaxis involves inositol 1,4,5-trisphosphate (1,4,5-IP3): micromolar amounts of 1,4,5-IP3 or Ca2+ were found to mimic the effects of chemoattractants and 1,4,5-IP3 triggered release of Ca2+ from non-mitochondrial stores. Here we report a more direct test of the involvement of inositol phosphates. Intact amoebae were labelled with high specific activity [3H]inositol, then stimulated with the chemoattractant cyclic AMP at 22 degrees C and rapidly assayed for phosphorylated inositol products formed. Labelled IP3 was found to accumulate transiently after a pulse of 50 nM-cyclic AMP, with a peak at 15 s after stimulation and some (inconclusive) evidence for a more rapidly formed peak at 5 s or less. Inositol bisphosphate (IP2) showed a transient shallow peak at about 20 s. When the events of signal transmission were slowed down by incubation at 4 degrees C, the rapidly formed IP3 peak could be consistently seen at 5 s after stimulation and the second peak at 25-30 s. Further resolution of the IP3 peaks indicated the presence of IP4, which represented a major fraction of the peak accumulated at 5 s (4 degrees C). The results provide an important link in the chain of evidence connecting the cell surface cyclic AMP receptors, via IP3, with the Ca2+-activated events of chemotaxis.

Chemotaxis of Spirochaeta aurantia: involvement of membrane potential in chemosensory signal transduction

The effects of valinomycin and nigericin on sugar chemotaxis in Spirochaeta aurantia were investigated by using a quantitative capillary assay, and the fluorescent cation, 3,3'-dipropyl-2,2'-thiodicarbocyanine iodide was used as a probe to study effects of chemoattractants on membrane potential. Addition of a chemoattractant, D-xylose, to cells in either potassium or sodium phosphate buffer resulted in a transient membrane depolarization. In the presence of valinomycin, the membrane potential of cells in potassium phosphate buffer was reduced, and the transient membrane depolarization that resulted from the addition of D-xylose was eliminated. Although there was no detectable effect of valinomycin on motility, D-xylose taxis of cells in potassium phosphate buffer was completely inhibited by valinomycin. In sodium phosphate buffer, valinomycin had little effect on membrane potential or D-xylose taxis. Nigericin is known to dissipate the transmembrane pH gradient of S. aurantia in potassium phosphate buffer. This compound did not dissipate the membrane potential or the transient membrane depolarization observed upon addition of D-xylose to cells in either potassium or sodium phosphate buffer. Nigericin did not inhibit D-xylose taxis in either potassium or sodium phosphate buffer. This study indicates that the membrane potential but not the transmembrane pH gradient of S. aurantia is somehow involved in chemosensory signal transduction.

Cyclic Nucleotide Changes in Human Neutrophils Induced by Chemoattractants and Chemotactic Modulators

Abstract Two classes of agents have effects on the chemotactic response of human neutrophils. Chemoattractants such as activated complement components, E. coli culture filtrates (BF) and the recently discovered N-formylmethionyl peptides, initiate directed movement, whereas chemotactic modulators enhance or depress cell movement initiated by chemoattractants. We and others have previously shown that cyclic AMP (cAMP) depresses neutrophil migration toward BF whereas cyclic GMP (cGMP) enhances the same process. In the present study, we examined the effects of several chemoattractants and chemotactic modulators on neutrophil levels of cGMP and cAMP. Trypsinized human complement, the E. coli BF and the synthetic peptide, formylmethionylalanine stimulated the accumulation of neutrophil cGMP (40 to 70% average increase) but had little effect on cAMP concentrations. The enhancing chemotactic modulators — phenylephrine, prostaglandin F2α, carbachol, and phorbol myristate acetate — also produced small (19 to 34%) but significant increases in PMN cGMP levels. In contrast, two agents which inhibit the chemotactic response, isoproterenol and prostaglandin E1, significantly elevated cAMP concentrations in PMN. These results suggest that the ability to elevate cGMP is inherent in the action of both chemoattractants and enhancing chemotactic modulators. Increases in cAMP appear to be correlated with inhibition of chemotaxis.

Effects of chemoattractants on the motility of Escherichia coli.

QUANTITATIVE studies of the chemotactic movements of flagellated bacteria have been reported recently1–5 and various details of the tactic response elicited by spatial gradients of certain sugars and amino acids have been established1–3. It has been shown, for example, that, over small ranges of chemo-attractant concentration, the chemotactic velocity is approximately proportional to the ratio of the gradient divided by the concentration (that is, Fechner's law)1–3. It is also known that response velocity depends on the absolute value of the chemoattractant concentration, increasing with values of attractant concentration up to a certain point (between 10−4 and 10−2 M, depending on the identity of the attractant), but then decreasing markedly at higher concentrations1–3.