Biomedical subjects

G M Omann

Publications and source records attributed to G M Omann.

At least 37 records · Page 2Linked to original sources

PubMed1995

Rapid oscillations of actin polymerization/depolymerization in polymorphonuclear leukocytes stimulated by leukotriene B4 and platelet-activating factor.

We previously showed that activation of polymorphonuclear leukocytes by leukotriene B4 (LTB4) and platelet-activating factor produces a rapidly oscillating actin polymerization/depolymerization response. In this study, we show that 1) oscillations are not due to the stimulated cyclic release of autocoids that could bind to cell surface receptors and activate subsequent cycles; 2) oscillations are not related to oscillations of ligand binding; and 3) the particular kinetic pattern is a property of the receptor, not of the binding constants of the ligand. The major conclusion of these studies is that the oscillations are a property of the intrinsic signaling pathways triggered by these chemoattractants. We also questioned whether increased actin nucleation activity was induced by LTB4 and found that, although LTB4 induced a transient actin nucleation response, there was not a direct correlation between oscillations of the actin polymerization/depolymerization and the actin nucleation activity. This suggests that processes other than actin nucleation, such as release of monomeric actin from monomer sequestering proteins and regulation of depolymerization, are likely to be involved.

Actins↗

PubMed1995

Desensitization of the actin polymerization response in human neutrophils at low cell density.

Many chemoattractant-activated responses in neutrophils show transient kinetics, suggesting that rapid desensitization occurs during the time course of the response. We found that desensitization of the actin polymerization response to N-formyl peptides is, in a large part, due to inhibition by adenosine released from cells to the medium and depletion or a chemical inactivation of the agonist. To reduce the influence of these factors, we stimulated neutrophils in a very diluted suspension, sometimes with continuous replacement of the medium. The actin polymerization response to a high agonist concentration was greatly enhanced and prolonged under these conditions, often without any tendency to subside within 10 min at 25 degrees C. It has previously been shown that the N-formyl peptide receptor converts from a rapidly dissociating to a slowly dissociating and presumably inactive form during activation. Under the conditions of low cell concentration, the conversion to a slowly dissociating receptor still occurred. Thus the prolonged response was not due to prolonged presence of rapidly dissociating receptors. We conclude either that a low number of rapidly dissociating receptors, which we failed to see, is sufficient to maintain actin polymerization or that slowly dissociating receptors can support the actin response. In contrast to responses stimulated by high agonist concentrations, the responses to low concentrations of the agonists were transient. The results of other authors indicate that low concentrations of N-formyl peptides do not desensitize the receptors. Other mechanisms, which are specific for the actin polymerization response, must be involved in response termination to low concentrations of N-formyl peptides. Activation at low cell density will be a useful approach for studying other processes (Ca2+ elevation, oxidant production, etc.) and chemoattractants (leukotriene B4, interleukin 8, etc.) for which an understanding of the kinetics due to desensitization of the components of the receptor-mediated activation pathway is desired.

Actin Cytoskeleton↗

PubMed1995

Ligand-receptor interaction rates in the presence of convective mass transport.

The rate of binding of a ligand to receptors on the cell surface can be diffusion limited. We analyze the kinetics of binding, diffusion-limited in a stationary liquid, in the presence of convective mass transport. We derive a formula that expresses the reaction kinetics in terms of the mass transfer coefficient. A moderately transport-limited kinetics is not readily recognizable from the shape of the binding curve and may lead to erroneous estimates of the rate coefficients. We apply our results to practically important cases: a cell suspension in a stirred volume of liquid and a confluent cell colony under a laminar stream. Using typical numbers characterizing the ligand-receptor interactions, we show that stirring and perfusion can be important factors determining the reaction rates. With the confluent colony, the early reaction kinetics requires a different treatment, and we provide it for the case of low receptor occupancy. We show that, even with a fast perfusion, a cell monolayer can transiently generate a zone of depletion of the ligand, and that would affect the early stages of the reaction. Our results are expressed in a simple analytical form and can be used for the design and interpretation of experimental data.

Animals↗

PubMed1994

H2O2-induced increases in cellular F-actin occur without increases in actin nucleation activity.

Previous work has shown that H2O2 causes an increase in polymerized actin (F-actin) inside cells. To test the hypothesis that increased polymerization resulted from a mechanism involving increased actin nucleation activity, we employed methods utilizing pyrene-labeled actin to quantify the actin nucleation activity of cell lysates and N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD)-phallacidin binding assays to quantify the amount of F-actin in P388D1 cells. H2O2 increased polymerized actin (NBD-phallacidin assay) in a dose-dependent manner with an effective dose giving 50% response (ED50) approximately 1 mM. Five millimolar H2O2 caused a 1.6-fold increase in NBD-phallacidin staining. In contrast, actin nucleation activity decreased in a dose-dependent manner with a similar ED50. Five millimolar H2O2 caused a 30-40% decrease in actin nucleation activity. The effect was rapid, occurring within 5 min of H2O2 addition. The results indicate that H2O2 causes cytoskeletal changes that enhance NBD-phallacidin binding without increasing actin nucleation activity. Fractionation studies showed that the nucleation activity in H2O2-treated cells and controls sedimented with the Triton X-100-insoluble cytoskeleton, and the cytosolic fraction appeared to contain an inhibitor of actin polymerization.

Actins↗

PubMed1993

A cellular model of oxidant-mediated neuronal injury.

Oxidants derived from the partial reduction of oxygen are thought to play a significant role in neuronal injury. We present here a cellular model of neuronal injury mediated by hydrogen peroxide (H2O2) using the PC 12 rat pheochromocytoma cell line. The organization of microtubules and microfilaments within neurites of PC 12 cells differentiated by exposure to nerve growth factor was examined after H2O2 injury using fluorescence microscopy. Concentrations of H2O2 as low as 100 microM produced an initial periodic pattern of microtubule depolymerization over 3-4 h which later progressed to complete depolymerization. Neuritic microspikes containing actin filaments were relatively more resistant to injury by H2O2 than microtubules. Blebbing of PC 12 cell bodies and neurites also was seen after H2O2 injury and the blebs appeared to contain microtubules. The destructive changes affecting neuritic structure preceded but were not essential for PC 12 cell lysis. Exposure of the cells to the Ca2+ ionophore, ionomycin (25 microM) also produced the same pattern of microtubule depolymerization in PC 12 neurites as was seen after H2O2 injury suggesting that H2O2 may mediate its destructive effect on the neurites via elevation of intracellular Ca2+.

Actin Cytoskeleton↗

PubMed1993

ATP depletion induces an increase in the assembly of a labile pool of polymerized actin in endothelial cells.

Depletion of cellular ATP is associated with profound effects on the cytoskeleton, particularly disruption of microfilaments. We examined this process in bovine pulmonary artery endothelial cells by inducing differential reductions of cellular ATP using mitochondrial inhibition and variable amounts of glucose. Reduction of cellular ATP to levels < 40% of control produced discrete stages in the visible disruption of microfilaments. Using the deoxyribonuclease I assay, a reversible 11% decrease in monomeric (G) actin occurred in conjunction with microfilament disruption. Polyacrylamide gel electrophoretic (PAGE) analysis of the detergent-insoluble cytoskeleton did not reveal any differences in actin content between normal or ATP-depleted cells. Image analysis of adherent endothelial cells that had been fixed and stained with N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-phallacidin revealed that an increase of F-actin of approximately 20% occurred in cells depleted of ATP. If the cells were lysed with detergent before fixation, the increase in F-actin was lost. PAGE analysis and electron microscopy of detergent-soluble material from the cells obtained by ultracentrifugation directly demonstrated the presence of a labile pool of F-actin within the cells, which increased with ATP loss. These observations suggest that ATP may play an important role in the organization and remodeling of microfilaments within cells.

Actin Cytoskeleton↗

PubMed1992

Inhibition of organic anion transport in endothelial cells by hydrogen peroxide.

ATP loss is a prominent feature of cellular injury induced by oxidants or ischemia. How reduction of cellular ATP levels contributes to lethal injury is still poorly understood. In this study we examined the ability of H2O2 to inhibit in a dose-dependent manner the extrusion of fluorescent organic anions from bovine pulmonary artery endothelial cells. Extrusion of fluorescent organic anions was inhibited by probenecid, suggesting an organic anion transporter was involved. In experiments in which ATP levels in endothelial cells were varied by treatment with different degrees of metabolic inhibition, it was determined that organic anion transport was ATP-dependent. H2O2-induced inhibition of organic anion transport correlated well with the oxidant's effect on cellular ATP levels. Thus H2O2-mediated inhibition of organic anion transport appears to be via depletion of ATP, a required substrate for the transport reaction. Inhibition of organic anion transport directly by probenecid or indirectly by metabolic inhibition with reduction of cellular ATP levels was correlated with similar reductions of short term viability. This supports the hypothesis that inhibition of organic anion transport after oxidant exposure or during ischemia results from depletion of ATP and may significantly contribute to cytotoxicity.

Adenosine Triphosphate↗

PubMed1992

A threshold level of coupled G-proteins is required to transduce neutrophil responses.

Chemoattractant-induced activation of human polymorphonuclear leukocytes involves receptor coupling to guanine nucleotide binding proteins (G-proteins). Treatment of polymorphonuclear leukocytes with pertussis toxin, which ADP-ribosylates neutrophil G-proteins and uncouples G-proteins from receptors, causes a conversion of cells from responders to nonresponders rather than a gradual decrease in the ability of all cells to respond (Omann, G. M., and J. M. Harter. 1991. Cytometry 12:252; Omann, G. M., and M. M. Porasik-Lowes. 1991. J. Immunol. 146:1303). Flow-cytometric methods were used to measure N-formylpeptide-induced cytosolic Ca2+ elevation and actin polymerization over a wide range of ADP-ribosylation levels and showed that although the percentage of responding cells varied markedly, the responding cells were stimulated equivalent to controls. The conditions of pertussis toxin (PT) treatment did not interfere with non-G-protein-mediated pathways as assessed by measurement of phagocytosis, a complex process involving the cytoskeleton. We tested the explanation that the all-or-none effect may have been due to heterogeneous insertion of the catalytic subunit of PT into the cells such that responders had no ADP-ribosylation and nonresponders were completely ADP-ribosylated. Measurement of the binding of fluorescent N-formylpeptides to permeabilized cells, which allows the distinction between completely ribosylated and normal cells, showed that all cells treated with a submaximal concentration of PT had intermediate levels of receptor-coupled G-proteins. Thus, partial ADP-ribosylation had occurred in all cells and the all-or-none insertion of the catalytic subunit of PT was ruled out. Thus, there is a threshold of coupled G-proteins required to transduce responses. The ability of PT to inhibit N-formylpeptide-induced actin polymerization and cytosolic calcium elevation was compared and showed that both responses have essentially the same threshold of G-proteins required to transduce the responses. Thus, the pathways regulating actin polymerization and calcium elevation appear to be coupled with equal efficiency to the G-proteins.

Actin Cytoskeleton↗

PubMed1992

Specific G proteins mediate endothelin induced contraction.

Endothelin is a potent vasoconstrictor peptide which has recently been localized in the gastrointestinal tract. We have investigated the transmembrane signaling properties of endothelin in isolated smooth muscle cells of the rabbit rectosigmoid. Endothelin induced a dose dependent contraction of smooth muscle cells in a range of 10(-10) to 10(-6)M. In normal buffer, contraction peaked at 30 sec and was sustained for up to 8 min. Incubation in 0Ca/2mM EGTA abolished the sustained contraction induced by endothelin, but had no effect on the initial transient contraction. Preincubation of saponin treated cells with G protein antisera had no effect on control cell length. Preincubation of saponin treated isolated smooth muscle cells with specific G protein antisera (rabbit antisera) for Go alpha or Gs for 60 minutes did not inhibit contraction induced by endothelin. Preincubation with an antiserum to Gi3 alpha inhibited the initial transient contraction induced by endothelin and preincubation with an antiserum to Gi1-2 alpha inhibited the sustained phase of the endothelin induced contraction. Our data indicate that: 1) Endothelin induces a direct sustained contraction of smooth cells from the rectosigmoid; 2) The transmembrane signalling of endothelin is through two specific GTP binding components that are Gi alpha, one for the initial transient contraction, and the other for the sustained phase of the contraction.

Animals↗

PubMed1991

Dual effects of guanosine 5'-[gamma-thio]triphosphate on secretion by electroporated human neutrophils.

It is generally believed that G-proteins play stimulatory roles on cell activation. In contrast, we found that guanosine 5'-[gamma-thio]triphosphate (GTP[S]) was a potent inhibitor of Ca(2+)-induced secretion from specific granules (as monitored by vitamin B-12-binding protein). GTP[S] inhibition of specific-granule release occurred in the presence or absence of adenine nucleotides, required Mg2+ (1-3 mM), and was half-maximal at 30 microM-GTP[S]. The dual stimulatory and inhibitory effects of GTP[S] could be readily observed and differentiated when degranulation was monitored over a range of Ca2+ concentrations. Inhibition of specific-granule release by GTP[S] was observed at low Ca2+ concentrations and resulted from shifting the Ca2+ dose-response curves to the right. In contrast, GTP[S] promoted azurophil-granule secretion at relatively high concentrations of Ca2+ and appeared to be due to a general enhancement at all Ca2+ concentrations. A series of hydrolysable and non-hydrolysable nucleotides did not mimic GTP[S] or block its action. Inhibition by GTP[S] occurred in cells which were sensitized with a protein kinase C agonist, suggesting that inhibition of secretion took place distal to this enzyme. However, the inhibitory effects of GTP[S] on specific-granule secretion were reversed by cytochalasin D, which prevents new microfilament formation; this compound also enhanced the stimulation of azurophil-granule release by GTP[S]. We also found that GTP[S] greatly increased the F-actin content of permeabilized neutrophils, whereas Ca2+ (to a lesser extent) decreased F-actin. These data are consistent with the hypothesis that at least two G-proteins are involved in regulating secretion: one which has been previously described as stimulating Ca(2+)-induced secretion (particularly from azurophil granules) and a second, possibly involved in promoting microfilament assembly, which inhibits the discharge of specific granules.

Actins↗

PubMed1991

Graded G-protein uncoupling by pertussis toxin treatment of human polymorphonuclear leukocytes.

Pertussis toxin (PT) inhibits polymorphonuclear leukocyte (PMN) function by ADP-ribosylating and inactivating guanine nucleotide binding proteins (G-proteins) that transduce activation by chemoattractants such as N-formyl peptides (FP). Studies of PMN activation during the time course of PT treatment yielded these results. 1) Responses were differentiated based on their sensitivity to PT treatment. Suboptimal PT treatment that resulted in 50% inhibition of the FP-induced actin-associated right angle light scatter response resulted in greater than 90% inhibition of oxidant production. Exhaustive PT treatment was required to completely inhibit the right angle light scatter response. This is consistent with previous observations that, relative to oxidant production, actin polymerization requires 100-fold fewer active N-formylpeptide receptors to elicit the response. This differential sensitivity to PT treatment has important implications for studies that use pertussis toxin to determine if the neutrophil G-protein is involved in the signaling of responses. If inhibition of oxidant production is used as the only indicator of the effectiveness of PT treatment, significant cytoskeletal changes may still be activated in these cells. Inhibition of actin polymerization is a much more rigorous indicator of complete G-protein inhibition by PT. 2) Analysis of FP-induced actin polymerization and cytosolic calcium elevation using flow cytometry, which measures individual cell responses, revealed that PT treatment resulted in the conversion of PMN from a responding to a non-responding population. In contrast, in control PMN, submaximal doses of FP caused submaximal stimulation of all the cells. The all-or-none effect of PT may result from heterogeneous insertion of the A-promoter of PT into the cell or it may result from a sharp threshold of coupled G-proteins required to transduce the responses.

Actins↗

PubMed1991

Intracellular calcium changes associated with in vitro lymphokine-activated killer and natural killer cell cytotoxicity.

Interleukin 2-activated peripheral blood lymphocytes (lymphokine-activated killer [LAK] cells) have been shown to lyse tumor cells in a nonspecific fashion. Although the mechanisms involved in this cell-mediated lysis are unknown, previous work has shown that T-lymphocyte-mediated cytolysis is associated with massive fluctuations in the intracellular calcium concentration within target cells. Studies were undertaken to determine whether intracellular calcium concentration changes were associated with LAK-mediated cytotoxicity and to determine the effects of calcium channel blockade on in vitro cell-mediated cytotoxicity. Natural killer (NK) and LAK cell cytotoxicity in vitro were measured against head and neck squamous cell carcinoma (UMSCC-11a and UMSCC-38) and Daudi cell lines. Assays were performed in parallel with flow cytometry to measure changes in intracellular calcium concentration within the target cells. Compared with NK cells, LAK cells showed enhanced cytotoxicity against the UMSCC-11a and Daudi lines but not the UMSCC-38 cell line. Both NK and LAK cell cytotoxicity against all the target cell lines directly paralleled significant increases in calcium concentration in the target cells. The addition of verapamil hydrochloride inhibited the rise in intracellular calcium concentration in the sensitive target cells and significantly inhibited both NK and LAK cell cytotoxicity in all the cell lines. The NK cell activity was more sensitive than LAK cell activity to verapamil inhibition. These data suggest that changes in the target cell calcium concentration are early and important events in both NK and LAK cell cytotoxicity in vitro.

Calcium↗

PubMed1991

Pertussis toxin effects on chemoattractant-induced response heterogeneity in human PMNs utilizing Fluo-3 and flow cytometry.

Flow cytometric methods were utilized to determine N-formylpeptide-induced cytosolic calcium levels in human polymorphonuclear leukocytes (PMNs) detected with the calcium indicator Fluo-3. Fluo-3 was readily loaded into PMNs as the acetoxymethyl ester. At room temperature Fluo-3 extrusion was minimal (less than 10%) over a 2 h time period. Flow cytometric histograms yielded symmetric distributions indicating homogeneous labelling of the cells. Stimulation of the cells with N-formyl-met-leu-phe (FMLP) caused homogeneous activation of all cells as indicated by a shift of the fluorescence distribution to higher fluorescence levels while still maintaining a symmetrical distribution. Resting values or FMLP-induced cytosolic calcium levels were similar in cells loaded over a 20-fold range of Fluo-3-acetoxymethyl ester. The effect of graded pertussis toxin (PT) treatment on the calcium response was determined by incubating cells with different concentrations of pertussis toxin for a time period that yielded a range of ADP ribosolation levels inside the cells. When these cells were activated with FMLP, the fluorescence histograms showed that pertussis toxin treatment resulted in a conversion of cells from responders to nonresponders. The responding cells responded with maximum calcium elevations similar to controls. This behavior may reflect heterogeneous insertion of the A-protomer of PT or a very sharp threshold of coupled G-proteins required to transduce the responses.

Aniline Compounds↗

PubMed1991

Flow cytometric analysis of human erythrocytes: II. Possible identification of senescent RBC with fluorescently labelled wheat germ agglutinin.

In the first paper of a series (Gutowski, et al., 1991) we discussed the use of flow cytometry to follow at the cellular level the aging of red blood cells (RBC) in circulation, using fluorescently labelled lectins and goat anti-human-IgG and -IgM. The Coulter Epics 541 was used for those studies. In this report we describe more extensive experiments using the Becton-Dickinson FACScan flow cytometer, and compare the results with those obtained with the Coulter Epics 541. By changing sample conditions from isotonic to hypotonic, compensation for differences of the two instruments was accomplished. We confirmed our previous observations that RBC react very strongly with fluorescein isothiocyanate labelled wheat germ agglutinin (FITC-WGA) and that there is little change in the intensity of fluorescence given by RBC of all sizes with the exception of the smallest. Reactivity with FITC-WGA is markedly decreased in the presence of competitive inhibitors of sialic acid or upon enzymatic removal of sialic acid from RBC. Removal of sialic acid is accompanied by increased reaction with peanut agglutinin (FITC-PNA). Flow cytometry was also used to monitor the enrichment of a population of smallest RBC (less than 0.05%), isolated from both counterflow centrifugation and the interface obtained from Histopaque separation. These smallest RBC showed low reactivity with FITC-WGA and higher binding of FITC-goat-anti-human-IgG, and -IgM, and therefore represent the most senescent RBC, just prior to their clearance from circulation by the reticuloendothelial system. These observations are in compliance with the hypothesis that physiological desialylation of glycophorin is responsible for clearance of senescent RBC from circulation (Aminoff, 1988).

Cellular Senescence↗

PubMed1990

Kinetics and amplification in neutrophil activation and adaptation.

Neutrophil activation and adaptation are beginning to be understood in quantitative and mechanistic detail. Neutrophil responses to chemoattractants involve cell surface receptors, guanine nucleotide binding (G) proteins and intracellular second messengers which are generated within a few seconds of the presentation of the ligand. Novel real-time fluorescent methods have made it possible to examine the dynamics of assembly and disassembly of receptors and G proteins during cell activation and to model, by computer, the complex sequence of ligand-receptor events. Rapid amplification cascades of signals are observed in both stimulatory and inhibitory receptor pathways. The adaptation of neutrophils involves uncoupling between receptors and G proteins, both by sequestering receptors from the transduction sequence and by reducing the activatibility of the G proteins.

Adaptation, Physiological↗

PubMed1989

Oscillating actin polymerization/depolymerization responses in human polymorphonuclear leukocytes.

Leukotriene B4 and platelet-activating factor induced a rapidly oscillating actin polymerization/depolymerization response in human polymorphonuclear leukocytes. N-Formylpeptides were deficient in the ability to induce these oscillations. Flow cytometric analysis of filamentous actin verified that all cells were synchronously responding in this cyclic manner. The hypothesis was tested that these oscillations were analogous to chemical oscillations, i.e. oscillations of intermediate species in chemical systems that are far from equilibrium (Epstein, I. R., Kustin, K., DeKepper, P., and Orban, M. (1983) Sci. Am. 248, 112). Actin polymerization/depolymerization cycles were terminated by adding receptor antagonist a few seconds after initiation of the response by agonists. Thus the oscillations did not represent chemical oscillations that hypothetically could result from a rapid jump of the intracellular milieu to a state far from equilibrium. Rather, continued occupancy of receptors and/or occupancy of new receptors was required to sustain the oscillations. This suggested that the oscillations resulted from regulated polymerization and depolymerization pathways. In simultaneous measurements of actin-associated right angle light scatter and intracellular calcium, no calcium oscillations were detected. Thus, cycles of actin polymerization/depolymerization were not regulated by calcium oscillations.

Actins↗

PubMed1989

Transient increase in phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol trisphosphate during activation of human neutrophils.

We recently showed that phosphatidylinositol trisphosphate (PIP3) was present in a unique lipid fraction generated in neutrophils during activation. Here, we demonstrate that the band containing this fraction isolated from thin layer chromatography consists primarily of PIP3 and that only small amounts of radiolabeled PIP3 exist prior to activation. In addition, high performance liquid chromatography of deacylated phospholipids from stimulated cells reveals an increase in a fraction eluting ahead of glycerophosphoinositol 4,5-P2. After removal of the glycerol we found that it coeluted with inositol 1,3,4-P3 when resubjected to high performance liquid chromatography. Thus, we have detected a second, novel form of phosphatidylinositol bisphosphate in activated neutrophils, PI-(3,4)P2. The elevation of PIP3 through the formyl peptide receptor is blocked by pretreatment with pertussis toxin, implicating mediation of the increase in PIP3 by a guanosine triphosphate-binding (G) protein. The rise in PIP3 is not secondary to calcium elevation. Buffering the rise in intracellular calcium did not diminish the increase in PIP3. The elevation of PIP3 appears to occur during activation with physiological agonists, its level varying with the degree of activation. Leukotriene B4, which elicits many of the same responses as stimulation of the formyl peptide receptor but with minimal oxidant production, stimulates a much attenuated rise in PIP3. Isoproterenol, which inhibits oxidant production also reduces the rise in PIP3. Hence formation of PI(3,4)P2 and PIP3 (presumed to be PI(3,4,5)P3) correlates closely with the early events of neutrophil activation.

Autoradiography↗

PubMed1988

Response of neutrophils to stimulus infusion: differential sensitivity of cytoskeletal activation and oxidant production.

The response of human neutrophils to N-formyl peptides were studied under conditions where ligand binding was controlled by infusing a cell suspension with the peptide over a time period comparable to the normal half-time for binding. Receptor occupancy was measured in real time with a fluorescently labeled peptide using flow cytometry. This binding was approximated by a simple reversible model using typical on (7 X 10(8) M- min-1) and off (0.35/min) rate constants and the infusion rates (0.02-0.2 nM/min). Under conditions of stimulus infusion intracellular calcium elevation, superoxide generation, and right angle light scatter and F-actin formation were measured. As the infusion rate was decreased into the range of 10 pM/min, lowering the rate of increase of receptor occupancy to approximately 0.5% per min, the calcium and right angle light scatter responses elongated in time and decreased in magnitude. Superoxide generation decreased below infusion rates of approximately 100 pM/min (occupancy increasing at a rate in the range of 5% per min). This behavior could contribute to differences between chemotactic responses, which appear to require low rates of receptor occupancy over long periods, and bactericidal or inflammatory responses (free radical generation and degranulation), which require bursts of occupancy of several percent of the receptors.

Actins↗