Transient increases in cytosolic free calcium appear to be required for the migration of adherent human neutrophils

Feedback regulation of cell-substratum adhesion by integrin-mediated intracellular Ca2+ signaling

Integrin binding to extracellular matrix (ECM) regulates cell migration and gene expression in embryogenesis, metastasis, would healing, and the inflammatory response. In many cases, binding of integrins to ECM triggers intracellular signaling pathways. The regulatory roles of intracellular signaling mechanisms in these events are poorly understood. Using single-cell analysis, we demonstrate that beads coated with peptide containing Arg-Gly-Asp (RGD), an integrin recognition motif found in many ECM proteins, elicit a rapid transient increase in intracellular calcium in Madin-Darby canine kidney (MDCK) epithelial cells. Also, significantly more beads bind to responding cells than to nonresponders. Several independent methods that inhibit RGD-induced Ca2+ signaling decrease both the number of beads bound and the strength of adhesion to an RGD-coated substratum. These results indicate that intracellular Ca2+ signaling participates in a positive feedback loop that enhances integrin-mediated cell adhesion.

Subtypes of inositol 1,4,5-trisphosphate receptor in human hematopoietic cell lines: dynamic aspects of their cell-type specific expression

Inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ signaling plays important roles in cellular responses to extracellular stimuli. We recently succeeded in cloning human counterparts of the three subtypes derived from separate genes. Using the cDNA sequences type-specific to these subtype receptors, we here analyzed the expression profile of IP3R subtypes in stimulated and unstimulated human hematopoietic cell lines representing T cells, B cells, neutrophils, macrophages, erythrocytes and megakaryocytes. Northern and dot blot analysis showed that each IP3R subtype is expressed differently in these cells and that the expression profile in each cell is dynamically changed upon stimuli which induce differentiation. Moreover, most of these cells were found to simultaneously express at least two different subtype receptors.

Involvement of S100-related calcium-binding protein pEL98 (or mts1) in cell motility and tumor cell invasion

We examined the relationship between cell motility and the expressions of pEL98 (mts1) mRNA and protein in various murine normal and transformed cells. The expression of pEL98 (mts1) in v-Ha-ras-transformed NIH3T3 cells and in normal rat kidney cells transformed by either v-Ha-ras or v-src was increased over that in the corresponding parental cells at both mRNA and protein levels. The expression in normal rat fibroblasts (3Y1) transformed by v-Ha-ras was also increased compared with that in 3Y1 cells. However, the expression of pEL98 (mts1) in 3Y1 cells transformed by v-src was increased in one clone (src 3Y1-K), but decreased in another clone (src 3Y1-H). The expression level of pEL98 (mts1) correlated well with cell motility, which was examined by measuring cell tracks by phagokinesis. In order to test direct involvement of the pEL98 (mts1) protein in cell motility, src 3Y1-H cells that showed low cell motility were transfected with pEL98 cDNA. The transfectants expressing large amounts of the pEL98 protein showed significantly higher cell motility than src 3Y1-H cells. The expression of pEL98 (mts1) was also found to be correlated with motile and invasive abilities in various clones derived from Lewis lung carcinoma. These results suggest that the pEL98 (mts1) protein plays a role in regulating cell motility and tumor cell invasiveness.

Interferon-gamma modulates cytosolic free calcium in human neutrophilic granulocytes

To investigate the role of cytosolic free calcium ([Ca2+]i in interferon-gamma (IFN-gamma) pre-activation (priming) of human neutrophilic granulocytes (PMN) we used three different fluorescence methods, i.e. digital imaging of single, adherent, Fura-2 loaded cells, flow cytometric measurements of single, non-adherent, Fluo-3 loaded cells, and spectrofluorometry of Indo-1 loaded PMN in suspension. IFN-gamma increased the [Ca2+]i level in single, adherent PMN during the second phase of the fMLP response. The bacterial peptide fMLP (N-formyl-L-methionyl-L-leucyl-L-phenylalanine) is a known stimulant of the calcium/inositol phosphate system. The [Ca2+]i increase was abolished in Ca(2+)-free test buffer. Furthermore, the baseline [Ca2+]i level was found to be slightly increased in IFN-gamma primed PMN as analysed with flow cytometry. On the other hand, these [Ca2+]i responses were not detectable with the other methods used. We suggest that IFN-gamma increases the plasma membrane permeability for calcium in PMN, and substantiate this by demonstrating compliance with a capacitative model for intracellular calcium regulation. Mathematical modeling also suggested that IFN-gamma primed human PMN may sequester 13% more Ca2+ than unprimed cells in fMLP-insensitive intracellular stores. Thus, the Ca2+ responses to IFN-gamma are modest and not easily detectable with some of the methods currently in use. They nevertheless explain why fMLP elicits brisker responses from PMN after IFN-gamma priming.

Bacterial endotoxin induces [Ca2+]i transients and changes the organization of actin in microglia

We have employed amoeboid microglia purified from primary cultures of neonatal rat brain to examine the effect of bacterial lipopolysaccharide (LPS), a potent activator of immune cells, on intracellular calcium concentration ([Ca2+]i) in brain macrophages. In single brain macrophages loaded with indo 1, pulse administration of LPS elicited a rapid and transient increase in [Ca2+]i. From a total of 70 cells examined, all responded to LPS with a similar [Ca2+]i transient, indicating a good homogeneity of the cell population with regard to the LPS response. It was concluded that the rise of cytosolic [Ca2+]i originated from intracellular stores because the response to LPS occurred similarly in the presence or in the absence of extracellular Ca2+. A second administration of LPS to the same cells resulted in a second but reduced [Ca2+]i transient. In contrast to the first response to LPS, this second response was totally dependent on the presence of Ca2+ in the extracellular medium. The first response to LPS was strongly inhibited by ruthenium red and could be suppressed in a reversible manner by preincubating the cells with caffeine in the absence of Ca2+ in the extracellular medium. These results indicate that caffeine-sensitive intracellular Ca2+ stores may be the major source of Ca2+ in the response of brain macrophages to LPS. The possible release of Ca2+ from phosphatidylinositol(3,4,5)-trisphosphate (IP3)-sensitive stores in brain macrophages was also evaluated by stimulating cells with the IP3-mobilizing agonist histamine. Brain macrophages were heterogeneous with regard to the histamine response since histamine induced a [Ca2+]i rise in only 30% of cells examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Critical role for intracellular calcium in tight junction biogenesis

Using the Madin Darby canine kidney (MDCK) cell "calcium switch," we have previously demonstrated that, as MDCK cells establish contact and ultimately form tight junctions, there are marked global and localized changes in intracellular calcium at the sites of cell-cell contact (Nigam et al., 1992, Proc. Natl. Acad. Sci. USA, 89:6162-6166). We have now examined whether intracellular Ca++ is critical to the biogenesis of tight junctions by chelating this ion and monitoring the formation of junctions by electrical, immunocytochemical, and biochemical criteria. Intracellular Ca++ was chelated with the cell-permeant chelators, dimethyl-BAPTA-AM and BAPTA-AM. By digital imaging of fura-2 loaded cells, it was demonstrated that both agents efficiently chelated Ca++ during the "switch" in a dose-dependent manner which paralleled their respective in vitro affinities for Ca++. Chelation of Ca++ during the switch markedly attenuated the development of transepithelial electrical resistance (TER), a measure of tight junction assembly. Immunofluorescent staining of the tight junctional protein, zonula occludens-1 (ZO-1), revealed that chelation of intracellular Ca++ retarded the movement of ZO-1 from intracellular sites to the plasma membrane during the switch. During the development of tight junctions, a fraction of ZO-1 redistributed from the Triton X-100 soluble to the Triton X-100 insoluble pool; chelation of Ca++ during the induction of cell-cell contact prevented this stabilization into the Triton X-100 insoluble fraction. Taken together, these data indicate an important role for intracellular Ca++ in tight junction biogenesis and suggest a specific role for calcium in the early sorting and possible cytoskeletal association of tight junction components.

Characterization of chemical gradients in the collagen gel-visual chemotactic assay

Chemical gradients developing in a collagen gel-visual chemotactic assay (CG-VCA) for PMNs were evaluated by theoretical and experimental methods. First, a video image analysis system was used to establish the diffusion coefficients of bromophenol blue (BPB) through the membrane (D1) and across the collagen gel (D2) in a capillary tube apparatus used only for this purpose. The diffusion coefficients of BPB and the geometry of the CG-VCA system were then used to develop a mathematical model, estimating theoretical gradients in the CG-VCA system. In addition, gradients in the CG-VCA system were characterized experimentally by employing BPB as the source and determining the concentration profiles of BPB in the chemotactic compartment by video image analysis. A relative error of approximately 21% exists between the theoretical and experimental gradients for both 0.5 and 1.0 mM source concentrations of BPB. This favorable comparison demonstrates reliability in predicting chemical gradients for the CG-VCA system. The mathematical model was then used to predict gradients using nanomolar and micromolar concentrations of low molecular weight chemoattractants. Analysis of these specific gradients showed that gradients were steep enough to be detected by PMNs in the collagen gel during the observation period used in previous experiments. The determination of BPB gradients in the CG-VCA system illustrates the utility of this system.

Ca2+ oscillations in neutrophils triggered by immune complexes result from Ca2+ influx

Although the mechanisms of Ca2+ signalling in neutrophils by certain chemotactic agents have been well characterized, the signalling by immune complexes is poorly understood. Here we demonstrate that immune complex stimulation, acting via Fc receptors, leads to repetitive Ca2+ spiking in neutrophils. Although the initial Ca2+ rise was the result of release of Ca2+ from intracellular stores, subsequent repetitive Ca2+ spikes resulted from transmembrane influx, as they were prevented by removal of extracellular Ca2+ and were accompanied by Mn2+ influx. The transmembrane Ca2+ spikes induced dramatic neutrophil cell shape changes. The Ca2+ spiking phase was inhibited by a phospholipase C (PLC) inhibitor, U73122, and removal of immune complex, but not by cytochalasin B. It was concluded that Ca2+ spiking was dependent upon the initial release of Ca2+ from an intracellular Ca2+ store, and driven by continued binding of immune complex, which triggered pulsatile changes in transmembrane influx.

Calcium-mediated signal transduction: biology, biochemistry, and therapy

The process of proliferation, invasion and metastasis is a complex one which involves both the autonomy of the malignant cells and their interaction with the cellular and extracellular environments. The way in which the tumor cells respond to cellular and extracellular stimuli is regulated through transduction of those signals and translation into cellular activity. Transmembrane signal transduction involves three major categories of events: ion channel activation, transmission through guanine nucleotide binding protein intermediates with production of second messengers, and phosphorylation events. A frequent common denominator of these different pathways is a cellular calcium homeostasis. Calcium may be both a result of and a regulator of many of these signal transduction pathways and has been shown to have a role in the regulation of proliferation, invasion, and metastatic potential. The understanding and application of the basic tenets of these pathways to tumor cell proliferation, invasion, and metastases opens a new target for therapeutic intervention. We have identified a novel agent, CAI, which through inhibition of stimulated calcium influx inhibits proliferation and migration in vitro, and growth and dissemination in human cancer xenografts in vivo. CAI offers a new approach to cancer therapy, signal transduction therapy.

Mechanisms of leukocyte motility and chemotaxis

Motility is a complex process that depends on the coordination of many cellular functions, including the conversion of information from the environment into a series of coordinated responses that culminate in directed cell movement. Major advances have been made in the understanding of many functions involved in motility, such as transmembrane signaling events, leading to alterations in the actin cytoskeleton, and interactions between adhesion receptors and components of the cytoskeleton, providing a link between the extracellular and intracellular environments. Studies using yeast (Saccharomyces cerevisiae), slime molds (Dictyostelium discoideum) and nematodes (Caenorhabditis elegans) have advanced our understanding of the molecular biology of cytoskeletal proteins and have important implications for mammalian leukocyte motility.

Human neutrophil motility: time-dependent three-dimensional shape and granule diffusion

The locomotion of human polymorphonuclear leukocytes (PMNs) was studied with two complementary methods: Three-dimensional shapes were reconstructed from time series of optical sectioning microscopy using differential interference contrast (DIC) optics, and the diffusion of cytoplasm granules within individual cells was measured using quasielastic laser light scattering (QELS). The three-dimensional cell edges outlined in the optical sections were analyzed qualitatively in time-lapse film strips and quantitatively from morphometry. The fastest locomotion occurred in chemotactic gradient with cell velocity that oscillated between 10 and 30 microns/min with a period of 50-55 seconds. Within the periodic bursts of speed, a fibroblast-like locomotory cycle was observed, with leading lamella extended and contacts formed with the substrate surface, followed by rapid motion of the cell body and nucleus over the immobile contacts. Consistent with this apparent staged motion, correlation analysis revealed a phase lag of 2-3 seconds in velocities between the bottom (ventral) and the top layers of the cell. In addition there was a tendency to a lower cell profile at times of higher velocity. The diffusion of natural cytoplasmic granules within resting PMNs was not affected by cytoskeleton disrupting drugs. During the stage of most rapid motion, when cytoplasmic streaming could be seen, diffusion of the granules decreased two- to 2.5-fold, and then returned to resting levels. These observations suggest that PMN locomotion consists of extensions near the surface to form forward contacts and then stiffening or possibly contraction of the cytoskeleton when the body of the cell is moved forward. Three-dimensional movies of PMN cells are included in the video supplement.

Beta 2 integrin engagement triggers actin polymerization and phosphatidylinositol trisphosphate formation in non-adherent human neutrophils

Beta 2 integrins are involved in the adhesion of leukocytes to other cells and surfaces. Although adhesion is required for cell locomotion, little is known regarding the way beta 2 integrin-receptors affect the actin network in leukocytes. In the present study filamentous actin (F-actin) levels in non-adherent human neutrophils have been measured by phalloidin staining after antibody cross-linking of beta 2 integrins. Antibody engagement of beta 2 integrins resulted in a rapid and sustained (146 and 131% after 30 and 300 s, respectively) increase in the neutrophil F-actin content. This is in contrast to stimulation with N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP), which causes a prompt and pronounced but rapidly declining rise in F-actin (214 and 127% after 15 and 300 s, respectively). Priming neutrophils with 1 nM PMA, a low concentration that did not influence the F-actin content per se, increased the magnitude of the beta 2 integrin-induced response but had no effect on the kinetics (199% after 30 s and 169% after 300 s). Removal of extracellular Ca2+ only marginally affected the beta 2 integrin-induced F-actin response for cells that were pretreated with PMA whereas the response for nonprimed cells was reduced by half. This suggests that even though extracellular Ca2+ has a modulatory effect it is not an absolute requirement for beta 2 integrin-induced actin polymerization. beta 2 integrin engagement did not affect the resting cellular level of cAMP arguing against a role of cAMP in beta 2 integrin-induced actin assembly.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotaxis of newt eosinophils: calcium regulation of chemotactic response

Local chemical events underlying chemotaxis were characterized in a new model cell, the newt eosinophil. These cells exhibit a chemotactic response to a trypsin-sensitive component of newt serum. Ca2+ plays a role in this process, since treatments expected to diminish Ca2+ availability from the medium [ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, Co2+, and verapamil], to break down transmembrane Ca2+ gradients (ionomycin), or to interfere with the function of intracellular Ca2+ stores (caffeine and neomycin) inhibited cell polarization and movement. Using imaging techniques we found that cytosolic Ca2+ concentration ([Ca2+]i) increased in response to newt serum. Migrating newt eosinophils exhibited a dynamic heterogeneous distribution of [Ca2+]i. [Ca2+]i was elevated in cells undergoing a change of direction relative to cells migrating persistently in one direction. Migrating cells contained gradients of [Ca2+]i along their long axis, with the front of the cell having consistently lower [Ca2+]i than the rear. When cells were loaded with the cell-permeant form of fura 2, fura 2 acetoxymethyl ester, a caffeine-sensitive membrane-delimited region of elevated [Ca2+]i was seen associated with the microtubule organizing center. A model is proposed relating the distribution of [Ca2+]i and the location of the external stimulus to the generation and interaction of substances within the cell that both simulate and inhibit increases in [Ca2+]i.

Flow cytometry reveals different lag times in rapid cytoplasmic calcium elevations in human neutrophils in response to N-formyl peptide

Flow cytometric analyses were performed to study intracellular single-cell calcium transients ([Ca2+]i) in suspended human neutrophils during the initial phase of N-formyl peptide stimulation. Thereby, two neutrophil populations became apparent. Early maximally Ca(2+)-responding (high fluorescence) neutrophils and not-yet Ca(2+)-responding (low fluorescence) neutrophils, but no neutrophils with intermediate levels of [Ca2+]i were detected. Within 7 s the number of low fluorescence neutrophils decreased and the number of high fluorescence neutrophils increased maximally. This suggests that [Ca2+]i transients occurred abruptly in individual neutrophils within a time interval below 1 s. At lower N-formyl peptide concentrations the lag times of individual neutrophils and the interval time of maximal activation of the [Ca2+]i-responding neutrophil population increased, however the percentage of [Ca2+]i-responding cells decreased. Surprisingly, no influence of the N-formyl peptide concentration on the [Ca2+]i-induced fluorescence signal of the individual cell was observed: it was always in an almost maximal range or not responding. In parallel, binding studies performed with fluorescein-labeled N-formyl peptide revealed that the heterogeneity of [Ca2+]i-responding cells cannot be explained by different receptor occupancy. In summary, this study demonstrates that [Ca2+]i transients induced by N-formyl peptides in suspended individual human neutrophils occur very rapidly in an almost "all-or-none manner" and that the mean increasing fluorescence signal of a calcium indicator within a whole neutrophil population results from varying lag times of the individual cells, rather than from the mean simultaneous progress of many cells.

Regulation of leukocyte locomotion by Ca2+

Neutrophils migrate towards sites of inflammation and infection by chemotaxis. Their motility is dependent on the actin cytoskeleton and on adhesion to extracellular substrates, but how these are regulated in response to stimuli is not clear. This review focuses on the potential role of Ca(2+) as a second messenger in neutrophil motility. Several effects of Ca(2+) and Ca(2+)-binding proteins on the stability and crosslinking of actin polymers have been demonstrated in vitro. Nevertheless, the complex mechanism by which Ca(2+) regulates actin in neutrophils is not fully understood. In addition, intracellular Ca(2+) regulates the intergin-mediated adhesion of neutrophils to extracellular matrix.

Simultaneous calcium-dependent delivery of neutrophil lactoferrin and reactive oxygen metabolites to erythrocyte targets: evidence supporting granule-dependent triggering of superoxide deposition

Optical microscopic techniques have been utilized to study the deposition of lactoferrin, a specific granule marker, and superoxide anions into target erythrocytes during antibody-dependent phagocytosis. Previous studies from this laboratory have shown that the entry of superoxide anions into erythrocytes can be sensitively monitored with Soret band transmitted light microscopy. When neutrophils were incubated with BAPTA/AM, an intracellular Ca2+ chelator, they phagocytosed IgG-opsonized sheep red blood cells (SRBC) but did not affect the microscopically detected absorption of their Soret band. When these same erythrocytes were observed after the infusion of 20 microM ionomycin, a Ca2+ ionophore, 58% of the cell-bound SRBC targets were destroyed immediately. However, neutrophils from chronic granulomatous disease (CGD) patients were unable to affect the Soret absorption of erythrocyte targets under any conditions. These results suggest that a Ca2+ signal can participate in triggering superoxide deposition in targets. Since Ca2+ signals are known to participate in the exocytic release of granules, we tested the hypothesis that specific lactoferrin-bearing granules are delivered to targets in parallel with superoxide anions. Lactoferrin delivery to phagosomes was monitored using resonance energy transfer (r.e.t.) microscopy. SRBCs were opsonized with both unconjugated and rhodamine B isothiocyanate (RBITC)-conjugated rabbit anti-SRBC IgG. After incubation with adherent neutrophils, the samples were washed, fixed with 3.7% paraformaldehyde, then labeled with fluorescein isothiocyanate (FITC)-conjugated antilactoferrin IgG. Energy transfer between FITC and RBITC was imaged microscopically and quantitated by photon counting. Significant levels of r.e.t. between antilactoferrin and anti-SRBC labels were observed after phagocytosis, but not in the absence of acceptor fluorochromes. To control for r.e.t. specificity, neutrophil membranes were labeled with FITC-conjugated, anti-HLA IgG after internalization of rhodamine B-tagged SRBCs (RSRBCs). Although r.e.t. between lactoferrin and RSRBCs labels was observed, no r.e.t. between HLA and RSRBC labels could be found. Further studies showed that treatment of neutrophils with BAPTA inhibited r.e.t. between anti-lactoferrin and RSRBCs. However, addition of ionomycin relieved this inhibition of energy transfer. These experiments show that both lactoferrin and superoxide delivery to targets are regulated in parallel by a Ca(2+)-dependent pathway. Furthermore, by combining Soret microscopy with r.e.t. microscopy, we have shown that superoxide anions and lactoferrin are delivered to the same phagosomes. We speculate that the NADPH oxidase, which produces superoxide anions, is assembled on specific granule membranes, thus accounting for their parallel Ca(2+)-dependence, activation, and delivery.

Spontaneously oscillating K+ channel activity in transformed Madin-Darby canine kidney cells

Intracellular alkalinization is known to be associated with tumorigenic transformation. Besides phenotypical alterations alkali-transformed Madin-Darby canine kidney (MDCK) cells exhibit a spontaneously oscillating cell membrane potential (PD). Using single-channel patch clamp techniques, it was the aim of this study to identify the ion channel underlying the rhythmic hyperpolarizations of the PD. In the cell-attached patch configuration, we found that channel activity was oscillating. The frequency of channel oscillations is 1.1 +/- 0.1 min-1. At the peak of oscillatory channel activity, single-channel current was -2.7 +/- 0.05 pA, and in the resting state it was -1.95 +/- 0.05 pA. Given the single-channel conductance of 53 +/- 3 pS for inward (and of 27 +/- 5 pS for outward) current the difference of single-channel current amplitude corresponded to a hyperpolarization of approximately 14 mV. The channel is selective for K+ over Na+. Channel kinetics are characterized by one open and by three closed time constants. The channel is Ca2+ sensitive. Half maximal activation in the inside-out patch mode is achieved at a Ca2+ concentration of 10 mumol/liter. In addition, we also found a 13-pS K+ channel that shows no oscillatory activity in the cell-attached patch configuration and that was not Ca2+ sensitive. We conclude that the Ca(2+)-sensitive 53-pS K+ channel is underlying spontaneous oscillations of the PD. It has virtually identical biophysical properties as a Ca(2+)-sensitive K+ channel in nontransformed parent MDCK cells. Hence, alkali-induced transformation of MDCK cells did not affect the channel protein itself but its regulators thereby causing spontaneous fluctuations of the PD.

F-actin content and spatial distribution in resting and chemoattractant-stimulated human polymorphonuclear leucocytes. Which role for intracellular free calcium?

Intracellular free calcium concentration ([Ca2+]i) plays a pivotal role for many responses in polymorphonuclear leucocytes (PMNs) stimulated by chemoattractants such as N-formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe). The importance of [Ca2+]i in the morphological polarization was investigated by using calcium-manipulated PMNs. We loaded human PMNs with BAPTA/AM to buffer or chelate [Ca2+]i in the presence or the absence of extracellular calcium by using fluo-3/AM as calcium indicator. The shape changes of PMNs were determined by microscopic examination, and membrane ruffling by right-angle light-scatter changes. Actin polymerization and F-actin distribution were recorded by staining PMNs with bodipy-phallacidin and quantified by quantitative fluorescence microscopy. We found that calcium-free incubation of PMNs loaded or not with 50 microM BAPTA/AM did not modify morphological polarization, membrane ruffling, actin assembly and F-actin distribution of PMNs stimulated with fMet-Leu-Phe, suggesting that these responses were probably functionally linked. It should be noted that incubation of PMNs in calcium-free conditions resulted in a radial distribution of F-actin and a moderate polymerization of actin, but not in morphological polarization of PMNs. Moreover, both calcium-sensitive and calcium-insensitive mechanisms of actin polymerization were additive, and inhibitable by 5 micrograms/ml cytochalasin B.

Agonist-stimulated Cl- efflux from human neutrophils. A common phenomenon during neutrophil activation

When human peripheral blood neutrophils were stimulated with various agonists which activate and/or prime neutrophils, we found that Cl- efflux was enhanced with a dramatic (50%) loss of intracellular Cl-. Interestingly, the Cl- efflux was enhanced by both agonists which induce a rapid transient increase in intracellular Ca2+ concentration ([Ca2+]i) [class I, e.g. N-formyl-methionyl-leucyl-phenylalanine (fMLP), interleukin-8 (IL8), platelet-activating factor, leukotriene B4 and C5a] and those which do not induce such an [Ca2+]i elevation [class II, e.g. tumor necrosis factor alpha (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF)]. The time course of agonist-stimulated Cl- efflux differed depending on the agonist. Class I agonists such as IL8 and fMLP exhibited a 1 min lag phase before the onset of Cl- efflux; class II agonists such as GM-CSF and TNF displayed a 2 and 5 min lag phase, respectively. Both IL8 (class I)- and TNF (class II)-stimulated Cl- efflux exhibited similar sensitivity to inhibition by different types of ion transport inhibitors [ethacrynic acid (EA), amiloride, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid, anthracene-9-carboxylic acid, and 4-4'-diisothiocyanatostilbene-2,2'-disulfonic acid]. On the other hand, natural Cl- efflux, which is thought to be mainly mediated by Cl-/Cl- self exchange, was not inhibited by EA (0.5 mM) or amiloride (0.3 mM). These results imply that both class I and class II agonist-stimulated Cl- efflux occurs via a common Cl- transporter which is different from that reported previously in resting human neutrophils. Although all agonists which induced a Cl- efflux also induced shape change of neutrophils, there did not appear to be a causal relationship between shape change and agonist-stimulated Cl- efflux. However, a temporal correlation was found to exist between agonist-stimulated Cl- efflux and intracellular alkalinization following agonist stimulation. Agonist-stimulated Cl- efflux therefore seems to be a common phenomenon activated by several agonists which act through different signal transduction pathways.

Assembly dynamics of actin in adherent human neutrophils

We have extended our previous studies of adherent neutrophils and compared actin depolymerization and intracellular calcium changes induced by adherence to laminin and fibronectin. In order to accurately assess cellular actin changes, F-actin depolymerization in the cell lysates must be inhibited. We found that phalloidin or 3.7% formaldehyde treatment effectively inhibited the depolymerization of F-actin fragments following cell lysis. Formaldehyde and phalloidin treatment reduced G-actin levels 75-80% in suspended cells, 35-73% in cells adherent for 1 min, and about 50% for cells adherent for 3 min. When the actin was fixed, there were highly significant differences in G-actin levels between the suspended and adherent cells as compared with unfixed cells. Adhesion to both laminin and fibronectin initiated a rapid rise in G-actin with a corresponding decrease in F-actin. However, the changes were more pronounced in cells adherent to laminin. The peak of depolymerization occurred by 1 min and, thereafter, G-actin decreased and F-actin increased reaching a steady state at 5 min. Adhesion to both laminin- and fibronectin-coated surfaces was accompanied by an increase of [Ca2+]i with a peak at 3 min, followed by a decrease from 3-5 min and a steady state attained between 5 and 10 min. The rise of [Ca2+]i in laminin-adherent cells was about twice that in fibronectin-adherent cells at 3 min (P < 0.02). Pertussis toxin, H-7, and staurosporin treatments did not alter the dynamic changes of actin in adherent cells, suggesting that these metabolic events are transduced by a G-protein and Protein Kinase C independent mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytosolic free Ca2+ signals in single adherent human neutrophils: generation and functional role

To study the role of cytosolic free calcium, [Ca2+]i, in cell activation, in particular during adhesion and movement on a surface in response to chemotactic peptide stimulation and during phagocytosis, we monitored [Ca2+]i in single human neutrophils. The neutrophils were loaded with fura-2 and allowed to adhere to albumin-coated glass coverslips. [Ca2+]i was monitored with a dual excitation microfluorimeter. Half of the cells showed spontaneous [Ca2+]i transients that lasted up to 15 min with an amplitude averaging 77 +/- 10 nM above basal levels (mean basal value of 110 +/- 20 nM) and a mean duration of 28 +/- 5 s. These repetitive [Ca2+]i elevations depended on the continuous presence of extracellular Ca2+ and could be dissociated from those triggered by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP). Cell morphology was monitored in parallel by recording fluorescent images with a high sensitivity charge coupled device (CCD) camera. The majority of the cells studied showed visible changes in shape which started either before or at the same time as the onset of the [Ca2+]i transients. Removal of extracellular Ca2+ abolished [Ca2+]i transients without impairing cell movement and spreading. Blockade of adherence and cell movement with cytochalasin B markedly inhibited [Ca2+]i transients. Monoclonal antibodies directed against the leucocyte integrin CR3 (CD11b/CD18 alpha m beta 2) blocked adherence, spreading and most of the [Ca2+]i activity. Total [Ca2+]i activity was assessed during phagocytosis of C3bi-opsonized yeast particles and correlated with fusion of secondary granules with the phagosomal membrane (P-L fusion).(ABSTRACT TRUNCATED AT 250 WORDS)

Recruitment of CD11b/CD18 to the neutrophil surface and adherence-dependent cell locomotion

Chemotactic stimulation of neutrophils results in translocation of CD11b/CD18 (Mac-1) from intracellular storage pools to the cell surface. Though results from several laboratories indicate that the newly arrived surface Mac-1 is not involved in the adherence induced by the initial stimulus, the present study addresses the hypothesis that this Mac-1 plays a role in subsequent adherence-dependent functions. The response of human neutrophils to changing concentrations of a chemotactic stimulus was evaluated by determining the amount of newly arrived surface Mac-1, and Mac-1-dependent adhesion and locomotion. Small step-wise increases in the concentration of f-Met-Leu-Phe (FMLP) resulted in proportional stepwise increases in surface Mac-1 that plateaued within 2-4 min. This newly arrived Mac-1 supported adhesion to protein-coated surfaces only when the cells were exposed to an additional increase in the FMLP stimulus level. Adherence-dependent cellular locomotion was evaluated in chambers that allowed rapid changes in the stimulus concentration. Repeated small increments in the stimulus level at 200-s intervals resulted in significantly longer migration paths than a single-step increase in the stimulus. The results support the hypothesis that small increments in the chemotactic stimulus bring Mac-1 to the cell surface, and this newly mobilized Mac-1 is available for adherence-dependent locomotion with subsequent increases in the concentration of the stimulus.

Isolation and characterization by cell density adjustment of a PC12 pheochromocytoma variant with altered Ca2+ homeostasis

Rat PC12 pheochromocytoma cells loaded with the fluorescent Ca2+ dye fluo-3 or indo-1 and scanned fluorimetrically on a cell sorter apparatus showed a rapid cell density-dependent increase in free cytosolic calcium concentration [Ca2+]i when maintained in suspension cultures. Cell adhesion, measured under a defined set of conditions, was low when cells were seeded at 1.5 x 10(4) cells/ml but reached maximal levels after addition of A23187 calcium ionophore. A six to sevenfold increase in cell density mimicked the effect of the ionophore. Densities above 2 x 10(6) cells/ml caused a decrease in cell adhesion, which was further reduced by the addition of A23187. BAPTA, AM (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) and nifedipine (10 microM each), partially inhibited cell attachment (34% and 44% reduction), but at 0.25 microM and 1 microM, respectively, they enhanced attachment (46% and 67% increase). The data suggest that a certain permissive level of [Ca2+]i, attained by either increasing cell density or by the presence of a calcium ionophore, is sufficient for maximal cell adhesion. Above the permissive level, manipulation of [Ca2+]i either by altering cell density or by the addition of calcium blocking agents in high concentrations results in a significant reduction in cell adhesion. Based on these observations, we were able to isolate a biochemically and morphologically distinct cell population. The variant, designated PC12ds (density selected), differed substantially from the original cells. Most notable was a relatively lower content of free [Ca2+]i in the PC12ds cells, as independently assayed by using fluo-3 and indo-1 dyes. In addition, the variant cells exhibited a significantly diminished rate of 45Ca2+ uptake, most likely due to less efficient L-type voltage-dependent calcium (VDC) channels. Addition of several calcium channels agonists and antagonists suggested that PC12ds cells contained relatively more N-type VDC channels, possibly indicating a shift to a neuronal phenotype.

A novel neutrophil-activating factor released by Trichomonas vaginalis

We have investigated the effects of a novel neutrophil-activating factor released by Trichomonas vaginalis (TV-NAF) on neutrophil chemotaxis. TV-NAF was present in the supernatant from 10(7) T. vaginalis (STV) cultured in 1 ml of serum-free Hanks' balanced salt solution (HBSS) at 37 degrees C for 30 min. With a multichamber chemotactic assay, we found that there were 112 +/- 15 migrated neutrophils (mean +/- standard deviation, n = 7) for STV and 11 +/- 4 for HBSS per high-power field (x 400). STV was also able to induce neutrophil actin assembly (increased 1.5-fold), enhance expression of complement receptor type 3 (increased 5-fold), and promote intracellular calcium mobilization (increased 2.5-fold). There was no chemotactic activity in the preparation of STV from killed trichomonads. The fact that heating up to 100 degrees C or deproteinization by treatment with proteinase K at 65 degrees C for 1 h did not abolish its chemotactic activity suggests that the TV-NAF involved was not a protein. The chemotactic activity of TV-NAF was associated with the fraction containing small molecules of less than 3,000 Da. Therefore, the possibility that eicosanoid production by trichomonads is responsible for neutrophil activation was investigated. Leukotriene B4 (LTB4; 500 pg/ml) but not thromboxane B2 (< 20 pg/ml) or prostaglandin E2 (< 8 pg/ml) was found in the STV by radioimmunoassay. Production of LTB4 by trichomonads was time dependent and increased twofold when arachidonic acid (100 microM) was added but was not decreased when eicosanoid inhibitors were present. Evidence for the presence of LTB4 in STV was further provided by the fact that rabbit anti-LTB4 antiserum could abolish the chemotactic activity of STV. These studies suggest that the spontaneous release of TV-NAF, which is most likely LTB4, may activate neutrophils, presumably through a different arachidonate metabolic pathway than that in mammalian cells.

Inhibition of neutrophil chemokinesis on vitronectin by inhibitors of calcineurin

Migration of human polymorphonuclear neutrophils on vitronectin is dependent on repeated transient increases in the concentration of intracellular free calcium ([Ca2+]i). A specific peptide inhibitor of the Ca(2+)-calmodulin-dependent phosphatase calcineurin was introduced into the cytoplasm of neutrophils. The peptide inhibited neutrophil migration on vitronectin by interfering with the release of the cells from sites of attachment. A similar reduction in motility on vitronectin occurred when cells were treated with the immunosuppressant FK506, which also inhibits calcineurin when bound to its binding protein, FKBP. These results indicate that a rise in [Ca2+]i reduces integrin-mediated adhesion to vitronectin by a mechanism that requires calcineurin activity.

Cytosolic free calcium is essential for immunoglobulin G-stimulated intracellular killing of Staphylococcus aureus by human monocytes

Earlier studies have shown that the intracellular killing of Staphylococcus aureus by human monocytes requires continuous stimulation by serum factors, e.g., immunoglobulin G (IgG). In the present study, we demonstrate that IgG, at concentrations that stimulate the intracellular killing of S. aureus, induces a transient increase in the intracellular free calcium concentration ([Ca2+]i) in monocytes. The Ca2+ ionophores A23187 and ionomycin stimulate the killing process as efficiently as IgG does and initiate O2- production in resting monocytes but not in monocytes containing bacteria. The Ca2+ ionophore-stimulated killing process was markedly inhibited by the NADPH oxidase inhibitor diphenyleneiodonium bisulfate, which indicates that these ionophores stimulate oxygen-dependent bactericidal mechanisms. Reduction of the [Ca2+]i to values below 1 nM, obtained by loading monocytes with MAPT/AM (1,2-bis-5-methyl-aminophenoxylethane-N,N,N',N'-tetraacetoxymet hyl acetate) in the absence of extracellular Ca2+, rendered the cells unresponsive to IgG or Ca2+ ionophore stimulation of the intracellular killing of S. aureus, but the response could be restored by reincubating these cells in the presence of extracellular Ca2+. It is concluded that cytosolic free Ca2+ is essential for the IgG-stimulated intracellular killing of S. aureus by human monocytes.

A novel principle for quantitation of fast intracellular calcium changes using Fura-2 and a modified image processing system--applications in studies of neutrophil motility and phagocytosis

A new principle is described for imaging intracellular free calcium [Ca2+]i changes in single, living cells utilizing the fluorescent probe Fura-2. It is based upon video color mixing in real time and allows high-speed visualization, at maximum image resolution, of [Ca2+]i changes without digital image ratioing. The epifluorescence images produced by 340 and 380 nm excitations are stored in two memory buffers of a personal computer-based image processing system. Two video signals are generated independently from each buffer and connected to the red and green inputs of a video display. An image is this way created, in which [Ca2+]i shows up as a specific hue, whereas changes in dye concentration, light intensity, cell thickness show up as variations in brightness of the imaged cells. The method has advantages over conventional ratio imaging, notably simplicity and speed, since no calculations are made. Yet it can be combined with traditional digital image processing. The imaging technique allows monitoring of [Ca2+]i changes in rapidly moving cells, like neutrophils. It is demonstrated that during random locomotion on serum-coated glass surfaces, [Ca2+]i levels appeared to oscillate and that the frequency of the oscillations are related to locomotive activity. Furthermore, in Ca2+ free medium, the cells continue to move and phagocytose in the presence of Ca2+ ionophore (ionomycin) and 2 mM EGTA. In the presence of 1 mM extracellular Ca2+, ionomycin-treated cells were not able to move or phagocytose.

Trypanosoma cruzi infection of BSC-1 fibroblast cells causes cytoskeletal disruption and changes in intracellular calcium levels

The disruption of vimentin and actin filaments of host BSC-1 fibroblast cells by Trypanosoma cruzi was investigated using a mouse monoclonal anti-vimentin antibody and rhodamine phalloidin, respectively. Indirect immunofluorescence microscopy demonstrated that infection of BSC-1 cells by T. cruzi caused disruption of both cytoskeletal components. The disruption was greater as infection progressed. Mechanisms other than mechanical ones may play a role in the disruption since disrupted cytoskeletal elements were well removed from the parasites. In the determination of intracellular calcium concentrations using Fura-2 AM, infected and uninfected cells both showed an initial increase in intracellular calcium levels. At later times of infection (3 to 5 days), intracellular calcium levels of infected cells were significantly lower than those of control cells. There was no specific localization of intracellular calcium in the infected host cells as determined by image analysis.

Intracellular ion imaging using fluorescent dyes: artefacts and limits to resolution

Development of highly efficient fluorescent ratio indicators has made imaging of ion concentrations within individual cells possible (Grynkiewicz et al. 1985; Tsien and Poenie 1986). Ion imaging is a complex technique and is therefore prone to artefacts. In this paper we investigate the limits of the technique and its potential pitfalls. The spatial resolution of an imaging system is determined for different cell geometries. We describe a technique to increase the time resolution of existing systems by using a single excitation wavelength to measure changes in ion concentration. We demonstrate examples of potential artefacts arising from hardware limitations, image processing and fundamental optics. Methods for recognition and minimization of these problems are discussed.

The role of calcium in neutrophil migration: the effect of calcium and calcium-antagonists in electroporated neutrophils

Chemotaxis by electroporated rabbit peritoneal neutrophils in the absence of Ca2+ is only slightly different from that in the presence of Ca2+. Pretreatment of neutrophils with quin2-AM causes inhibition of chemotaxis. Calcium antagonists as nitrendipine and verapamil are inhibitory in nanomolar concentrations, while 10(5) times higher concentrations are required for inhibition of chemotaxis by neutrophils which were not electroporated. The results support the hypothesis that Ca2+ from Ca(2+)-storing organelles is of importance for chemotaxis, but that chemotaxis is not dependent on changes in cytoplasmic Ca2+ concentrations.

Alteration in Ca2+ homeostasis by a trauma peptide

Postinjury tissue inflammation with PMN elastase proteolysis generates immunosuppressive fibronectin peptides (FNDP) impairing chemotaxis, T-cell activation, and proliferation. Excess intracellular Ca2+ ([Ca2+]i) impairs T-cell activation. This study quantifies the changes in [Ca2+]i following exposure to a degradation peptide of fibronectin to determine the mechanism of action of these peptides on calcium homeostasis. Isolated human PBLs were exposed to immunosuppressive concentrations of FNDP after loading with the [Ca2+]i probe FURA-2AM. Resting and sustained [Ca2+]i concentrations were calculated and compared to buffer control. The mechanism of action was determined by pretreatment with: (1) EDTA binding extra cellular Ca2+: [Ca2+]e, (2) the Ca2+ channel blockers verapamil and nifedipine, and (3) inhibition of [Ca2+]i released by dantrolene. Inositol triphosphate (IP3) essential for [Ca2+]i release was measured following T-cell stimulation as well. FNDP caused 200-400% increases in [Ca2+]i concentration relative to buffer control at known suppressive doses. Verapamil and nifedipine partially block [Ca2+]i influx by as much as 50% suggesting the slow Ca2+ (voltage independent) channels are partially responsible for the increased [Ca2+]i seen following FNDP. EDTA completely suppressed [Ca2+]e influx but did not completely inhibit the release of [Ca2+]i although IP3 was 80% suppressed. The increase in [Ca2+]i following FNDP stimulation is due to release of intracellular stores.

Inhibition of tumor cell invasion by verapamil

Verapamil, a calcium channel antagonist, inhibits murine B16 melanoma and colon adenocarcinoma C26 tumor metastasis by altering platelet aggregation [Tsuruo, T., et al. (1985) Cancer Chemother. Pharmacol., 14:30-33]. However, the role of calcium homeostasis in regulating several biochemical pathways implicated in other steps of the metastatic cascade suggests that calcium channel antagonists could also inhibit metastasis by other mechanisms. In this report, non-toxic doses of verapamil reversibly decreased human A375M and C8161 melanoma cell invasion and metastasis in a dose-dependent manner. Verapamil reduced cellular invasion and metastases by up to 96% (range 78-96%). Concomitantly, verapamil disrupts microtubule and microfilament organization and inhibits unidirectional cell migration but does not affect cellular adhesion to endothelial monolayers or reconstituted basement membranes. In addition, tumor cells treated with verapamil have a decrease in mRNA of type IV collagenase, a proteinase important in tumor cell degradation of basement membranes. Collectively, these data offer additional evidence regarding the mechanisms of action of verapamil as an anti-metastatic agent.

Calcium gradients underlying polarization and chemotaxis of eosinophils

The concentration of intracellular free calcium ([Ca2+]i) in polarized eosinophils was imaged during chemotaxis by monitoring fluorescence of the calcium-sensitive dye Fura-2 with a modified digital imaging microscope. Chemotactic stimuli caused [Ca2+]i to increase in a nonuniform manner that was related to cell activity. In cells moving persistently in one direction, [Ca2+]i was highest at the rear and lowest at the front of the cell. Before cells turned, [Ca2+]i transiently increased. The region of the cell that became the new leading edge had the lowest [Ca2+]i. These changes in [Ca2+]i provide a basis for understanding the organization and local activity of cytoskeletal proteins thought to underlie the directed migration of many cells.

Synchronous free Ca2+ changes in individual neutrophils stimulated by leukotriene B4

Calcium (Ca2+) signals were monitored in individual neutrophils using ratio imaging of fura-2. In contrast to N-formyl-L-leucyl-L-phenylalanine (f-met-leu-phe), which produced grossly asynchronous Ca2+ signals with delays in response (up to 60 s), leukotriene B4 (LTB4) provoked synchronous and immediate elevations in cytosolic free Ca2+. Some individual neutrophils which responded immediately to LTB4, subsequently displayed delayed Ca2+ signals in response to f-met-leu-phe. A sub-population of neutrophils failed to respond to both LTB4 and f-met-leu-phe. The asynchrony of the Ca2+ signalling to f-met-leu-phe is not, therefore, an obligatory property of signal transduction in neutrophils.

Calcium signaling capacity of the CD11b/CD18 integrin on human neutrophils

The CD11b/CD18 integrin is a major cell adhesion molecule of myelomonocytic cells. Exposure of human neutrophils in suspension to CD11b or CD18 monoclonal antibodies (mAbs)2 does not affect the resting level of cytosolic free Ca2+ in these cells; however, a subsequent cross-linking of either of these antibodies triggers a prompt and significant cytosolic-free Ca2+ transient lasting about 10 min. The rise in cytosolic-free Ca2+ (from 130 +/- 2 to 414 +/- 12 nM or 111 +/- 12 to 331 +/- 22 nM caused by cross-linking of CD11b or CD18 subunits, respectively) is due to both mobilization of Ca2+ from intracellular stores and influx of Ca2+ across the plasma membrane. Cross-linking of the common leukocyte antigen (CD45) did not alter the basal level of cytosolic free Ca2+. In accordance with other adherence-induced phenomena and with CD11/CD18-mediated phagocytosis, these Ca2+ signals were only modestly affected by pertussis toxin. Thus, the present data clearly indicate that the CD11b/CD18 integrin on human neutrophils is capable of inducing a prompt cytosolic-free Ca2+ signal. These findings directly support the recent suggestion that the CD11b/CD18 integrin is responsible for the "spontaneous oscillations" of cytosolic-free Ca2+ observed in adherent neutrophils and, at least partially, also explain how integrin-mediated adherence can modify the functional responsiveness of neutrophils to a subsequent agonist stimulation.

Extracellular ATP and some of its analogs induce transient rises in cytosolic free calcium in individual canine keratinocytes

Changes in intracellular free calcium ([Ca++]i) play an important role in a variety of biochemical reactions that lead to cellular responses such as proliferation and differentiation. The response of [Ca++]i to extracellular nucleotides (ATP, UTP, ITP, and AMP-PNP) was determined in individual canine keratinocytes using the fluorescent probe fura-2 and digital video fluorescence imaging microscopy. In the presence of 1.8 mM extracellular Ca++, 100 and 500 microM ATP caused a rapid (less than 9 sec) three- to twelvefold rise in [Ca++]i above resting levels of 50-150 nM followed by occasional fluctuations. Small responses were elicited with doses as low as 0.1 microM ATP. The response of cells stimulated with 500 microM ATP in Ca(++)-free medium was characterized by 1.5 to 3 times rapid initial peak followed by a decrease of [Ca++]i below resting levels. Loss of response occurred in the majority of keratinocytes preincubated for 30 min in Ca(++)-free medium. UTP was as effective as ATP in stimulating rises in [Ca++]i in keratinocytes. Smaller elevations in [Ca++]i up to four- to fivefold resting levels were noted with 100 microM AMP-PNP or 500 microM ITP. Desensitization of cells was demonstrated when a second stimulation followed the primary ATP or UTP treatment. These results are suggestive of the presence of purinergic receptors in the cytoplasmic membrane of canine keratinocytes. Experiments using the calcium channel blocker lanthanum suggest that ATP-induced initial rises and sustained levels of [Ca++]i are dependent on the release of Ca++ from intracellular stores. These intracellular Ca++ stores appear to be rapidly depleted after removal of extracellular calcium ([Ca++]e), thereby abolishing ATP-induced [Ca++]i increases.

A visual assay for quantitating neutrophil chemotaxis in a collagen gel matrix. A novel chemotactic chamber

The chemotactic behavior of polymorphonuclear leukocytes (PMNs) suspended in a three-dimensional gel of native collagen fibers was analyzed using a new visual assay aided by computer assisted tracking. Cell behavior was observed in a 7 microliters chamber closed at either end with capillary tubes tipped with dialysis membrane. The chemoattractant, LTB4, was placed in one capillary tube and the control substance in the opposite tube. Under microscopic observation neutrophils were videotaped, their images digitized, and the x and y coordinates of the cell centroids captured at 30 s intervals for 15 min and subsequently analyzed. The data generate a global perspective of neutrophil behavior in a medium simulating a collagenous tissue. The results show that when leukotriene B4 was substituted for HBSS the PMN population underwent chemotactic displacement. PMN chemotaxis was increased greatly when the concentration of LTB4 was increased from 10 nM to 1 microM in separate experiments. This result was partly achieved by movement of an increasing percentage of the PMN population, less frequent stops, and longer durations of motility for individual cells. The most dramatic effect of LTB4 on neutrophil behavior was a large increase in directional movement toward the chemotactic source. The effects of LTB4 fell dramatically when the gradient source concentration was increased to 10 microM. The visual assay described here provides clear evidence that LTB4 induces true neutrophil chemotaxis in a collagenous matrix.

Opposite effect of cytochalasin B on agonist-induced respiratory burst in neutrophils and monocytes

The effects of cytochalasin B on the respiratory burst, calcium transients and cell shape change of neutrophils and monocytes has been studied. Cytochalasin B enhanced fMLP-induced respiratory burst in neutrophils whereas the opposite effect, i.e. an inhibition close to 50%, was elicited in fMLP-stimulated monocytes. The differences did not depend on calcium homeostasis. On the basis of cell shape changes, and the well known effect of cytochalasin B on actin polymerization, the opposite effects of cytochalasin B could stem from differences between both cell types concerning the pattern of cytoskeleton-membrane interaction which could affect the recruitment and assembly of membrane-bound or cytosolic components of NADPH-oxidase.

Increased intracellular calcium is associated with progression of HPV-18 immortalized human keratinocytes to tumorigenicity

Studies were conducted using normal and human papillomavirus Type 18 (HPV-18) immortalized human keratinocytes to assess possible alterations in the differentiation process as a consequence of increased intracellular calcium concentration. Normal keratinocytes exposed to increased extracellular calcium or the phorbol ester TPA, exhibited terminal differentiation characteristics. However, late passage HPV-18 immortalized keratinocytes (designated FEP-1811) were resistant to such terminal differentiation signals. Flow cytometric analyses of 1811 cells at various stages of passage in culture revealed progressively higher levels of intracellular calcium in the immortalized cells with passage in culture when compared to normal, primary keratinocytes. Furthermore, 1811 cells isolated from tumors which developed in irradiated nude mice contained the highest level of intracellular calcium of all the cells examined. These results suggest that an increase in the concentration of intracellular calcium is associated with progression of HPV-18 immortalized keratinocytes to tumorigenicity.

Multiple elevations of cytosolic-free Ca2+ in human neutrophils: initiation by adherence receptors of the integrin family

Multiple spontaneous transient elevations of cytosolic-free calcium ([Ca2+]i) are observed in single human neutrophils during adherence. The interrelation between adherence and spontaneous [Ca2+]i transients was analyzed by simultaneous monitoring of [Ca2+]i and cell morphology. Fluorescent images of fura 2-loaded neutrophils attached to albumin-coated glass were recorded with a high sensitivity CCD camera while [Ca2+]i was assessed with a dual excitation microfluorimetry. The majority of the initially round cells studied showed changes in shape which started either before or at the same time as the onset of the [Ca2+]i transients. These data suggested that a rise in [Ca2+]i is not a prerequisite for shape change. This conclusion was confirmed by observation of movement and spreading in cells whose [Ca2+]i transients were abolished by chelation of extracellular Ca2+. Instead, our data suggest that spreading or adhesion itself initiates the [Ca2+]i activity. In keeping with this hypothesis, cytochalasin B, which prevents both cell movement and adhesion, completely inhibited generation of [Ca2+]i transients. To determine if the movement alone or adhesion alone is responsible for [Ca2+]i activity, we treated cells with antibodies against the beta chain (CD18, beta 2) or the alpha subunit (CD11b, alpha m) of the dominant leukocyte integrin (CR3). Antibody-treated cells showed normal extension of pseudopods but impaired ability to adhere. Inhibition of adhesion in this way inhibited [Ca2+]i activity. Taken together these results suggest that following sequence of events after contact of neutrophils with surfaces: (a) cell movement and shape change lead to enhanced contact of integrins with the surface; and (b) integrins-mediated adhesion generates multiple [Ca2+]i transients. The [Ca2+]i transients may then control exocytic events associated with movement and may provide a link between adherence and activation or priming of neutrophils to other stimuli.

Preparation of solutions with free calcium concentration in the nanomolar range using 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid

There are many uses for solutions with a known free calcium concentration ([Ca2+]free) in the nanomolar range. Most frequently ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) has been used as a buffer for the control of [Ca2+]free; however, under a variety of conditions the use of 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) for this purpose would be advantageous. The theory and calculations necessary to make solutions with known [Ca2+]free appropriate for given conditions of pH, ionic strength, and temperature for use with EGTA or BAPTA are reviewed. Practical considerations and methods for making such solutions are detailed. The advantages and disadvantages associated with the use of each of the two chelators are discussed. As one example of the application of solutions with free calcium in the nanomolar range, the dissociation constant of the fluorescent indicator fura-2 for calcium has been determined in a physiologic buffer at 22 and 37 degrees C. For practical reasons, the use of BAPTA is advantageous when solutions with different known [Ca2+]free must be used on a daily basis.

The involvement of calcium and protein kinase C in modulating agonist-stimulated chemotaxis of human neutrophils

Chemotaxis of human neutrophils in response to a gradient of the chemotactic peptide, fmet-leu-phe (FMLP), was measured by the under-agarose technique. The dose-response curve for FMLP was biphasic; low concentrations were stimulatory, and the response was reduced at higher concentrations. The response to FMLP was partially inhibited (about 50%) in the absence of extracellular Ca2 (EGTA added). NiCl2 dose-dependently inhibited FMLP-stimulated chemotaxis in the presence of extracellular Ca2+; the maximum inhibition obtainable with NiCl2 was similar to that with the absence of extracellular Ca2+. These results suggest that FMLP-stimulated chemotaxis is, at least partially, dependent on stimulation of Ca2+ influx. The phorbol ester, PMA, dose-dependently inhibited chemotaxis; the response was almost completely inhibited by 10 nM PMA. This result indicates that activation of protein kinase C inhibits chemotaxis. These results are discussed in relation to the physiological responses of neutrophils.

Roles of actin filaments and three second-messenger systems in short-term regulation of chick dorsal root ganglion neurite outgrowth

In a previous study (J. Cell Biol. 109: 1229-1243, 1989), we reported that conditions which increased growth cone calcium levels and induced neurite retraction in cultured chick DRG neurons also resulted in an apparent loss of actin filaments in the growth cone periphery. We further showed that the actin-stabilizing drug phalloidin could block or reverse calcium-ionophore-induced neurite retraction, indicating that the behavioral changes were mediated, at least in part, by changes in actin filament stability. In this study, we have further characterized the calcium sensitivity of growth cone behavior to identify which features of calcium-induced behavioral effects can be attributed to effects on actin filaments alone, and to assess whether two other second-messenger systems, cAMP and protein kinase C, might influence neurite outgrowth by altering calcium levels or actin stability. The results indicated that growth cone behavior was highly sensitive to small changes in calcium concentrations. Neurite outgrowth was only observed in calcium-permeabilized cells when extracellular calcium concentrations were between 200 and 300 nM, and changes as small as 50 nM commonly produced detectable changes in behavior. Furthermore, low doses of cytochalasins mimicked all of the grossly observable features of growth cone responses to elevation of intracellular calcium, including the apparent preferential destruction of lamellipodial actin filaments and sparing of filopodial actin, suggesting that the behavioral effects of calcium elevation could be explained by loss of actin filaments alone. The effects of cAMP elevation and protein kinase C activation on growth cone behavior, ultrastructure, and fura2-AM-measured calcium levels indicated that the effects of cAMP manipulations could be partially explained by a cAMP-induced lowering of growth cone calcium levels and concomitant increased stabilization of actin filaments, but protein kinase C appeared to act through an independent mechanism.