Refilling the inositol 1,4,5-trisphosphate-sensitive Ca2+ store in neuroblastoma x glioma hybrid NG108-15 cells

Neuronal Store-Operated Calcium Channels

The endoplasmic reticulum (ER) is the major intracellular calcium (Ca²⁺) storage compartment in eukaryotic cells. In most instances, the mobilization of Ca²⁺ from this store is followed by a delayed and sustained uptake of Ca²⁺ through Ca²⁺-permeable channels of the cell surface named store-operated Ca²⁺ channels (SOCCs). This gives rise to a store-operated Ca²⁺ entry (SOCE) that has been thoroughly investigated in electrically non-excitable cells where it is the principal regulated Ca²⁺ entry pathway. The existence of this Ca²⁺ route in neurons has long been a matter of debate. However, a growing body of experimental evidence indicates that the recruitment of Ca²⁺ from neuronal ER Ca²⁺ stores generates a SOCE. The present review summarizes the main studies supporting the presence of a depletion-dependent Ca²⁺ entry in neurons. It also addresses the question of the molecular composition of neuronal SOCCs, their expression, pharmacological properties, as well as their physiological relevance.

Negative regulation of chemokine receptor signaling and B-cell chemotaxis by p66Shc

Shc (Src homology 2 domain containing) adaptors are ubiquitous components of the signaling pathways triggered by tyrosine kinase-coupled receptors. In lymphocytes, similar to other cell types, the p52 and p66 isoforms of ShcA/Shc participate in a self-limiting loop where p52Shc acts as a positive regulator of antigen receptor signaling by promoting Ras activation, whereas p66Shc limits this activity by competitively inhibiting p52Shc. Based on the fact that many signaling mediators are shared by antigen and chemokine receptors, including p52Shc, we have assessed the potential implication of p66Shc in the regulation of B-cell responses to chemokines, focusing on the homing receptors CXCR4 (C-X-C chemokine receptor type 4) and CXCR5 (C-X-C chemokine receptor type 5). The results identify p66Shc as a negative regulator of the chemotactic responses triggered by these receptors, including adhesion, polarization and migration. We also provide evidence that this function is dependent on the ability of p66Shc to interact with the chemokine receptors and promote the assembly of an inhibitory complex, which includes the phosphatases SHP-1 (Src homology phosphatase-1) and SHIP-1 (SH2 domain-containing inositol 5'-phosphatase-1), that results in impaired Vav-dependent reorganization of the actin cytoskeleton. This function maps to the phosphorylatable tyrosine residues in the collagen homology 1 (CH1) domain. The results identify p66Shc as a negative regulator of B-cell chemotaxis and suggest a role for this adaptor in the control of B-cell homing.

Novel role for STIM1 as a trigger for calcium influx factor production

STIM1 has been recently identified as a Ca(2+) sensor in endoplasmic reticulum (ER) and an initiator of the store-operated Ca(2+) entry (SOCE) pathway, but the mechanism of SOCE activation remains controversial. Here we focus on the early ER-delimited steps of the SOCE pathway and demonstrate that STIM1 is critically involved in initiating of production of calcium influx factor (CIF), a diffusible messenger that can deliver the signal from the stores to plasma membrane and activate SOCE. We discovered that CIF production is tightly coupled with STIM1 expression and requires functional integrity of its intraluminal sterile alpha-motif (SAM) domain. We demonstrate that 1) molecular knockdown or overexpression of STIM1 results in corresponding impairment or amplification of CIF production and 2) inherent deficiency in the ER-delimited CIF production and SOCE activation in some cell types can be a result of their deficiency in STIM1 protein; expression of a wild-type STIM1 in such cells was sufficient to fully rescue their ability to produce CIF and SOCE. We found that glycosylation sites in the ER-resident SAM domain of STIM1 are essential for initiation of CIF production. We propose that after STIM1 loses Ca(2+) from EF hand, its intraluminal SAM domain may change conformation, and via glycosylation sites it can interact with and activate CIF-producing machinery. Thus, CIF production appears to be one of the earliest STIM1-dependent events in the ER lumen, and impairment of this process results in impaired SOCE response.

Calcium signaling in non-excitable cells: Ca2+ release and influx are independent events linked to two plasma membrane Ca2+ entry channels

The regulatory mechanism of Ca2+ influx into the cytosol from the extracellular space in non-excitable cells is not clear. The "capacitative calcium entry" (CCE) hypothesis suggested that Ca2+ influx is triggered by the IP(3)-mediated emptying of the intracellular Ca2+ stores. However, there is no clear evidence for CCE and its mechanism remains elusive. In the present work, we have provided the reported evidences to show that inhibition of IP(3)-dependent Ca2+ release does not affect Ca2+ influx, and the experimental protocols used to demonstrate CCE can stimulate Ca2+ influx by means other than emptying of the Ca2+ stores. In addition, we have presented the reports showing that IP(3)-mediated Ca2+ release is linked to a Ca2+ entry from the extracellular space, which does not increase cytosolic [Ca2+] prior to Ca2+ release. Based on these and other reports, we have provided a model of Ca2+ signaling in non-excitable cells, in which IP(3)-mediated emptying of the intracellular Ca2+ store triggers entry of Ca2+ directly into the store, through a plasma membrane TRPC channel. Thus, emptying and direct refilling of the Ca2+ stores are repeated in the presence of IP(3), giving rise to the transient phase of oscillatory Ca2+ release. Direct Ca2+ entry into the store is regulated by its filling status in a negative and positive manner through a Ca2+ -binding protein and Stim1/Orai complex, respectively. The sustained phase of Ca2+ influx is triggered by diacylglycerol (DAG) through the activation of another TRPC channel, independent of Ca2+ release. The plasma membrane IP(3) receptor (IP(3)R) plays an essential role in Ca2+ influx, by interacting with the DAG-activated TRPC, without the requirement of binding to IP(3).

The role of superoxide anions in the development of distant tumour recurrence

We hypothesise that reactive oxygen species (ROS) released from activated polymorphonuclear leucocytes during surgery play a crucial role in enhanced tumour recurrence seen after surgery. Therefore, the effect of ROS on adhesion of tumour cells to microvascular endothelium in a reproducible human in vitro model was studied. Preincubation of microvascular endothelial cells with the superoxide anion producing xanthine–xanthine oxidase complex significantly increased adhesion of the human colon carcinoma cells HT29 (167% vs control, P<0.01), Caco2 (164% vs control, P<0.01) and of the pancreas carcinoma cells PanC1 (180% vs control, P<0.01). Addition of the antioxidant enzymes superoxide dismutase or catalase significantly decreased tumour cell adhesion (P<0.01). Exposure of endothelial cells to superoxide anions increased the apoptotic rate to 7.9 times the normal rate. Additionally, exposure increased expression of the endothelial adhesion molecules E-Selectin, ICAM-1, and VCAM-1 of maximally 170% vs control (P<0.01). In conclusion, this study shows that superoxide anions promote the adherence of tumour cells to the microvasculature by inducing endothelial apoptosis that subsequently induces the expression of various adhesion molecules for tumour cells. This indicates that by tackling the production of ROS preventing tumour recurrence at distant sites might be feasible.

Phosphatidylinositol 3-kinase gamma signaling through protein kinase Czeta induces NADPH oxidase-mediated oxidant generation and NF-kappaB activation in endothelial cells

We addressed the role of class 1B phosphatidylinositol 3-kinase (PI3K) isoform PI3Kgamma in mediating NADPH oxidase activation and reactive oxidant species (ROS) generation in endothelial cells (ECs) and of PI3Kgamma-mediated oxidant signaling in the mechanism of NF-kappaB activation and intercellular adhesion molecule (ICAM)-1 expression. We used lung microvascular ECs isolated from mice with targeted deletion of the p110gamma catalytic subunit of PI3Kgamma. Tumor necrosis factor (TNF) alpha challenge of wild type ECs caused p110gamma translocation to the plasma membrane and phosphatidylinositol 1,4,5-trisphosphate production coupled to ROS production; however, this response was blocked in p110gamma-/- ECs. ROS production was the result of TNFalpha activation of Ser phosphorylation of NADPH oxidase subunit p47(phox) and its translocation to EC membranes. NADPH oxidase activation failed to occur in p110gamma-/- ECs. Additionally, the TNFalpha-activated NF-kappaB binding to the ICAM-1 promoter, ICAM-1 protein expression, and PMN adhesion to ECs required functional PI3Kgamma. TNFalpha challenge of p110gamma-/- ECs failed to induce phosphorylation of PDK1 and activation of the atypical PKC isoform, PKCzeta. Thus, PI3Kgamma lies upstream of PKCzeta in the endothelium, and its activation is crucial in signaling NADPH oxidase-dependent oxidant production and subsequent NF-kappaB activation and ICAM-1 expression.

Epigallocatechin-3-gallate increases intracellular [Ca2+] in U87 cells mainly by influx of extracellular Ca2+ and partly by release of intracellular stores

Green tea has been receiving considerable attention as a possible preventive agent against cancer and cardiovascular disease. Epigallocatechin-3-gallate (EGCG) is a major polyphenol component of green tea. Using digital calcium imaging and an assay for [3H]-inositol phosphates, we determined whether EGCG increases intracellular [Ca2+] ([Ca2+]i) in non-excitable human astrocytoma U87 cells. EGCG induced concentration-dependent increases in [Ca2+]i. The EGCG-induced [Ca2+]i increases were reduced to 20.9% of control by removal of extracellular Ca2+. The increases were also inhibited markedly by treatment with the non-specific Ca2+ channel inhibitors cobalt (3 mM) for 3 min and lanthanum (1 mM) for 5 min. The increases were not significantly inhibited by treatment for 10 min with the L-type Ca2+ channel blocker nifedipine (100 nM). Treatment with the inhibitor of endoplasmic reticulum Ca2+-ATPase thapsigargin (1 micro M) also significantly inhibited the EGCG-induced [Ca2+]i increases. Treatment for 15 min with the phospholipase C (PLC) inhibitor neomycin (300 micro M) attenuated the increases significantly, while the tyrosine kinase inhibitor genistein (30 micro M) had no effect. EGCG increased [3H]-inositol phosphates formation via PLC activation. Treatment for 10 min with mefenamic acid (100 micro M) and flufenamic acid (100 micro M), derivatives of diphenylamine-2-carboxylate, blocked the EGCG-induced [Ca2+]i increase in non-treated and thapsigargin-treated cells but indomethacin (100 micro M) did not affect the increases. Collectively, these data suggest that EGCG increases [Ca2+]i in non-excitable U87 cells mainly by eliciting influx of extracellular Ca2+ and partly by mobilizing intracellular Ca2+ stores by PLC activation. The EGCG-induced [Ca2+]i influx is mediated mainly through channels sensitive to diphenylamine-2-carboxylate derivatives.

Muscarinic calcium mobilization in the regenerating retina of adult newt

We used optical recording with a Ca(2+)-sensitive dye, fura2, in living slice preparations from the newt retina at different stages of regeneration. ACh produced the most pronounced [Ca2+]i rise in progenitor cells and premature ganglion cells of the earlier stage of retinal regeneration, but less pronounced Ca2+ response in ganglion cells just before, or at the beginning of, synaptogenesis. The [Ca2+]i rise to ACh was mediated by mAChRs. This was shown by inhibition of the ACh-induced Ca2+ response with a preincubation of the mAChR antagonist atropine as well as with direct stimulation of the [Ca2+]i rise by the mAChR agonist muscarine. This muscarine-induced [Ca2+]i rise was more greatly suppressed by the M1 and/or M3 preferring mAChR antagonists than by the M2 preferring mAChR antagonist. The [Ca2+]i rise due to muscarine was not suppressed in the absence of extracellular Ca2+, but suppressed in part in the presence of the L-type voltage-gated Ca2+ channel blockers, verapamil or nicardipine. Furthermore, thapsigargin (TG), a Ca-ATPase inhibitor, abolished the muscarine-induced [Ca2+]i rise in the absence of extracellular Ca2+. These results suggest that the mAChR-mediated [Ca2+]i rise is mainly a result of a release of Ca2+ from intracellular stores. TG produced a slow rise in the resting level of [Ca2+]i. This [Ca2+]i raise was suppressed as extracellular Ca2+ was omitted, whereas a rapid rise in [Ca2+]i occurred when extracellular Ca2+ was reintroduced, suggesting the occurrence of the capacitative Ca2+ influx in the progenitor cells and premature ganglion cells of the regenerating newt retina.

Endogenous somatostatin receptors mobilize calcium from inositol 1,4,5-trisphosphate-sensitive stores in NG108-15 cells

Somatostatin receptors are members of the G-protein-coupled receptor superfamily and exert their principal effects by coupling to inhibitory G-proteins. We used fura-2-based digital calcium imaging and assayed for [3H]inositol phosphates (IPs) to study the effects of somatostatin on intracellular calcium signaling in neuroblastomaxglioma NG108-15 cells. Both somatostatin-14 and octreotide induced concentration-dependent increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). Thirty-four percent of the cells responded to treatment with 100 nM somatostatin-14. Somatostatin-induced responses were not blocked by the removal of extracellular calcium; instead, they were abolished by pretreatment with 100 nM thapsigargin, an agent that depletes and prevents refilling of intracellular Ca(2+) stores. Pretreatment with the inositol 1,4,5-trisphosphate (IP(3)) receptor antagonist xestospongin C (10 microM) for 20 min inhibited markedly the somatostatin-induced response. Somatostatin (100 nM) increased [3H]IPs formation. U73122 (1 microM), an inhibitor of phospholipase C (PLC), completely blocked the somatostatin-induced [Ca(2+)](i) increases and the formation of [3H]IPs. Pretreatment with pertussis toxin (PTX, 200 ng/ml) for 24 h blocked the somatostatin-induced responses. Thus, we conclude that activation of endogenous somatostatin receptors in NG108-15 cells induces the release of calcium from IP(3)-sensitive intracellular stores through PTX-sensitive G-protein-coupled PLC.

Randomized, prospective trial of antioxidant supplementation in critically ill surgical patients

OBJECTIVE

To determine the effectiveness of early, routine antioxidant supplementation using alpha-tocopherol and ascorbic acid in reducing the rate of pulmonary morbidity and organ dysfunction in critically ill surgical patients.

SUMMARY BACKGROUND DATA

Oxidative stress has been associated with the development of the acute respiratory distress syndrome (ARDS) and organ failure through direct tissue injury and activation of genes integral to the inflammatory response. In addition, depletion of endogenous antioxidants has been associated with an increased risk of nosocomial infections. The authors postulated that antioxidant supplementation in critically ill surgical patients may reduce the incidence of ARDS, pneumonia, and organ dysfunction.

METHODS

This randomized, prospective study was conducted to compare outcomes in patients receiving antioxidant supplementation (alpha-tocopherol and ascorbate) versus those receiving standard care. The primary endpoint for analysis was pulmonary morbidity (a composite measure of ARDS and nosocomial pneumonia). Secondary endpoints included the development of multiple organ failure, duration of mechanical ventilation, length of ICU stay, and mortality.

RESULTS

Five hundred ninety-five patients were enrolled and analyzed, 91% of whom were victims of trauma. The relative risk of pulmonary morbidity was 0.81 (95% confidence interval 0.60-1.1) in patients receiving antioxidant supplementation. Multiple organ failure was significantly less likely to occur in patients receiving antioxidants than in patients receiving standard care, with a relative risk of 0.43 (95% confidence interval 0.19-0.96). Patients randomized to antioxidant supplementation also had a shorter duration of mechanical ventilation and length of ICU stay.

CONCLUSIONS

The early administration of antioxidant supplementation using alpha-tocopherol and ascorbic acid reduces the incidence of organ failure and shortens ICU length of stay in this cohort of critically ill surgical patients.

Role of neutrophil NADPH oxidase in the mechanism of tumor necrosis factor-alpha -induced NF-kappa B activation and intercellular adhesion molecule-1 expression in endothelial cells

In this study, we explored a novel function of polymorphonuclear neutrophils (PMN) NAD(P)H oxidase in the mechanism of tumor necrosis factor-alpha (TNFalpha)-induced NF-kappaB activation and intercellular adhesion molecule-1 (ICAM-1) expression in endothelial cells. Studies were made in mice lacking the p47(phox) subunit of NAD(P)H oxidase as well as in cultured mouse lung vascular endothelial cells (MLVEC) from these mice. In response to TNFalpha challenge, NF-kappaB activation and ICAM-1 expression were significantly attenuated in lungs of p47(phox)(-/-) mice as compared with wild-type (WT) mice. The attenuated NF-kappaB activation in p47(phox)(-/-) mice was secondary to inhibition of NIK activity and subsequent IkappaBalpha degradation. Induction of neutropenia using anti-PMN serum prevented the initial TNFalpha-induced NF-kappaB activation and ICAM-1 expression in WT mice, indicating the involvement of PMN NAD(P)H oxidase in signaling these responses. Moreover, the responses were restored upon repletion with PMN obtained from WT mice but not with PMN from p47(phox)(-/-) mice. These findings were recapitulated in MLVEC co-cultured with PMN, suggesting that NF-kappaB activation and resultant ICAM-1 expression in endothelial cells occurred secondary to oxidants generated by the PMN NAD(P)H oxidase complex. The functional relevance of the PMN NAD(P)H oxidase in mediating TNFalpha-induced ICAM-1-dependent endothelial adhesivity was evident by markedly reduced adhesion of p47(phox)(-/-) PMN in co-culture experiments. Thus, oxidant signaling by the PMN NAD(P)H oxidase complex is an important determinant of TNFalpha-induced NF-kappaB activation and ICAM-1 expression in endothelial cells.

Lactosylceramide mediates tumor necrosis factor-alpha-induced intercellular adhesion molecule-1 (ICAM-1) expression and the adhesion of neutrophil in human umbilical vein endothelial cells

The endothelial expression of adhesion molecules by proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) has been suggested to contribute to the initiation of atherosclerotic plaque formation. Since lactosylceramide (LacCer) accumulates in large quantities in human atherosclerotic plaque, we have explored its role in TNF-alpha-induced expression of intercellular adhesion molecule-1 (ICAM-1) in human umbilical vein endothelial cells and their consequent adhesion to polymorphonuclear leukocytes (PMNs). We found that TNF-alpha increased LacCer synthesis by way of stimulating the activity of UDP-galactose:glucosylceramide beta(1-->4)-galactosyltransferase in a time-dependent fashion. The TNF-alpha-induced expression of ICAM-1 was abrogated by D-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), an inhibitor of UDP-galactose:glucosylceramide beta(1-->4)-galactosyltransferase. However, the addition of LacCer reversed the D-PDMP effect on TNF-alpha-induced ICAM-1 expression in human umbilical vein endothelial cells. Northern hybridization analysis of mRNA levels and enzyme-linked immunosorbent assays revealed that LacCer (5 microM) specifically stimulated ICAM-1 at both the transcriptional and translational levels. This was accompanied by the adhesion of PMNs, which was visualized by confocal microscopy. Further studies revealed that LacCer stimulated the endogenous generation of superoxide radicals (O-2) about 5-fold compared with the control by specifically activating plasma membrane-associated NADPH-dependent oxidase. This phenomenon was blocked by the antioxidant N-acetyl-L-cysteine, pyrrolidine dithiocarbamate, and the NADPH oxidase inhibitor, diphenylene iodonium. Overexpression of endogeneous CuZn-superoxide dismutase via an adenoviral vector carrying cDNA for CuZn-superoxide dismutase, also inhibited LacCer-induced ICAM-1 expression in endothelial cells. In sum, our findings suggest that LacCer may play the role of a lipid second messenger in TNF-alpha-induced pathogenesis by activating an oxidant-sensitive transcriptional pathway that leads to the adhesion of PMNs to endothelial cells.

Desensitization of delta-opioid-induced mobilization of Ca2+ stores in NG108-15 cells

Activation of delta-opioid receptors in NG108-15 cells induces the release of calcium from an inositol 1,4,5-trisphosphate- sensitive intracellular store. We used fura-2-based digital imaging to study the effects of prolonged exposure to agonist on opioid-induced increases in [Ca2+]i. Exposure to D-Ala2-E-Leu5 enkephalin (DADLE) (1 microM) for 30 min completely desensitized NG108-15 cells to a second DADLE-induced response. The cells recovered gradually over 25 min following washout of DADLE. The desensitization was not due to depletion of intracellular calcium stores and bradykinin failed to cross-desensitize the DADLE-evoked response, although both agonists mobilized the same Ca2+ store. Desensitization induced by 100 nM DADLE was overcome by a higher concentration of DADLE (100 microM). Treatment with 8-cpt-cAMP (0.1 mM) for 30 min did not influence the DADLE-induced increases in [CA2+]i. Phorbol dibutyrate (PdBu) (1 microM) blocked the response completely. Treatment with the inhibitor of cyclic nucleotide-dependent kinases H8 (1 microM) for 45 min did not prevent DADLE-induced desensitization. Treatment with the protein kinase C (PKC) inhibitors staurosporin (10 nM) and GF-109203X (200 nM) for 45 min reduced desensitization. However, down-regulation of PKC by 24 h exposure to PdBu (1 microM) failed to prevent the DADLE-induced desensitization in NG108-15 cells. Thus, we conclude that multiple pathways participated in desensitization of delta-receptor-mediated Ca2+ mobilization, one of which includes PKC.

Ca2+ influx through voltage-gated Ca2+ channels regulates 5-HT3 receptor channel desensitization in rat glioma x mouse neuroblastoma hybrid NG108-15 cells

1. The kinetics of desensitization of the 5-HT3 receptor (5-HT3R)-gated ion channel were investigated using whole-cell and perforated-patch recording techniques in NG108-15 cells. 2. Rapid application of 5-HT (50 microM) elicited a 5-HT3R-mediated inward current response that desensitized completely in the continued presence of agonist. In the whole-cell recording configuration (holding potential of -70 mV) while buffering internal calcium (Cai2+) with 5 mM EGTA (0.5 mM added Ca2+; with an estimated free [Ca2+] of 30 nM), the rate of desensitization was initially rapid (with a half-time of approximately 230 ms), but dramatically slowed with time by 1120 +/- 160%. 3. This slowing in the rate of desensitization was reduced by stronger Ca2+ buffering (20 mM BAPTA, without added Ca2+), or by the bath application of cadmium (100 microM) to block voltage-gated Ca2+ channels. The rate of desensitization was also dependent on membrane potential. 4. In perforated-patch recordings, the rate of desensitization remained constant. However, a slowing in the desensitization rate could be induced by depolarizing cells immediately prior to the application of 5-HT. 5. The depolarization-induced slowing was blocked by incubating cells with BAPTA-AM (a membrane-permeant analogue of BAPTA) or by the bath application of cadmium. 6. These data suggest that Ca2+ influx through a cadmium-sensitive voltage-gated Ca2+ channel increases the cytoplasmic Ca2+ concentration ([Ca2+]i) and induces a dramatic slowing in the kinetics of desensitization of the 5-HT3R channel. These data provide evidence for cross-talk between voltage-gated Ca2+ channels and 5-HT3Rs in NG108-15 cells.

In vitro changes in capacitative Ca2+ entry in neuroblastoma X glioma NG108-15 cells

Changes in capacitative Ca2+ entry were studied in neuroblastoma x glioma NG108-15 cells with fura-2 fluorescence measurements in the following three culture conditions. The application of thapsigargin (250 nM) with a Ca2+-free solution depleted intracellular Ca2+ stores and the capacitative Ca2+ entry was induced by the addition of extracellular Ca2+ in the cells cultured in the medium for proliferation. The capacitative Ca2+ entry decreased in the cells cultured in the medium for neuronal differentiation. When these cells resumed proliferation after changing the culture media to the initial medium for proliferation, the capacitative Ca2+ entry increased again and exceeded the level in the initial proliferation state. These results suggested that the capacitative Ca2+ entry occurred more intensely at the proliferation state than at the neuronally differentiated state.

Differential regulation of interleukin-8 and intercellular adhesion molecule-1 by H2O2 and tumor necrosis factor-alpha in endothelial and epithelial cells

The reactive oxygen intermediate H2O2 can function as a signaling molecule to activate gene expression. In this study, we demonstrate that oxidant stress induced by tumor necrosis factor alpha (TNFalpha) or H2O2 differentially regulates intercellular adhesion molecule-1 (ICAM-1) and interleukin-8 (IL-8) gene expression in endothelial and epithelial cells. Northern blot analysis revealed that TNFalpha induced both ICAM-1 and IL-8 expression in either the A549 lung epithelial cell line or the human microvessel endothelial cell line (HMEC-1). In contrast, H2O2 selectively induced only ICAM-1 in HMEC-1 and only IL-8 in A549. This cell type-specific pattern of IL-8 expression was also observed in several other endothelial and epithelial cells. TNFalpha induced greater IL-8 gene expression as compared with H2O2, but the kinetics of induction were similar. The induction of epithelial IL-8 message was accompanied by a corresponding increase in functional IL-8 protein secretion as determined by a neutrophil motility assay. The increased neutrophil motility stimulated by conditioned media from H2O2- or TNFalpha-exposed A549 cells was completely inhibited by an anti-IL-8 antibody. TNFalpha and H2O2 also induced a differential pattern of CC chemokine expression in A549. While TNFalpha induced both RANTES and MCP-1, H2O2 induced only MCP-1. These data suggest that epithelial cells under oxidant stress contribute to the inflammatory cytokine network by selective production of IL-8, MCP-1, and RANTES, which may critically influence the site-specific recruitment of leukocyte subsets.

Cold ischemic injury accelerates the progression to chronic rejection in a rat cardiac allograft model

BACKGROUND

The pathogenesis of chronic rejection likely involves an interplay between immunogenic and nonimmunogenic factors. The objective of this study was to determine the influence of cold ischemic preservation injury on the rate of progression to chronic rejection in the Lewis to F344 cardiac allograft model.

METHODS

To induce an ischemic injury, donor hearts were stored for 3 hr at 4 degrees C in University of Wisconsin solution before transplantation. Allografts were excised at 1, 7, and 90 days after transplantation or at rejection. Vasculopathy was graded for degree of intimal thickening based on the involvement of vascular perimeter and luminal compromise.

RESULTS

The degree of vessel injury in ischemic injured allografts at 90 days was significantly greater than in nonischemic injured allografts (2.8+/-0.4 vs. 1.6+/-0.5, P<0.05). Ischemic injury in syngeneic grafts did not induce a vasculopathy. Immunoperoxidase staining with R73 (anti-T cell) and ED1 (anti-macrophage) monoclonal antibodies revealed that, in ischemic injured allografts at 90 days after transplantation, the infiltrate was composed predominantly of T cells and macrophages. Additionally, ischemic injured allografts excised at 7 days after transplantation showed cellular infiltrates composed of R73-positive T cells and rare interleukin-2 receptor-positive cells, which was not observed in nonischemic allografts or ischemic syngeneic grafts.

CONCLUSIONS

The progression to chronic vasculopathy in this model is principally an immunologic process, which is accelerated by an ischemic insult to the allograft. The vascular injury is mediated in part by T cells and macrophages.

Cyclic ADP-ribose enhances coupling between voltage-gated Ca2+ entry and intracellular Ca2+ release

Ca2+ release from intracellular stores can be activated in neurons by influx of Ca2+ through voltage-gated Ca2+ channels. This process, called Ca2+-induced Ca2+ release, relies on the properties of the ryanodine receptor and represents a mechanism by which Ca2+ influx during neuronal activity can be amplified into large intracellular Ca2+ signals. In a differentiated neuroblastoma cell line, we show that caffeine, a pharmacological activator of the ryanodine receptor, released Ca2+ from intracellular stores in a Ca2+-dependent and ryanodine-sensitive manner. The pyridine nucleotide, cyclic ADP-ribose, thought to be an endogenous modulator of ryanodine receptors also amplified Ca2+-induced Ca2+ release in these neurons. Cyclic ADP-ribose enhanced the total cytoplasmic Ca2+ levels during controlled Ca2+ influx through voltage gated channels, in a concentration-dependent and ryanodine-sensitive manner and also increased the sensitivity with which a small amount of Ca2+ influx could trigger additional release from the ryanodine-sensitive intracellular Ca2+ stores. Single cell imaging showed that following the Ca2+ influx, cyclic ADP-ribose enhanced the spatial spread of the Ca2+ signal from the edge of the cell into its center. These powerful actions suggest a role for cyclic ADP-ribose in the functional coupling of neuronal depolarization, Ca2+ entry, and global intracellular Ca2+ signaling.

Capacitative Ca2+ influx in the neural retina of chick embryo

Depletion of intracellular Ca2+ stores induces a capacitative Ca2+ influx in non-neural cells. It has been unknown whether the capacitative Ca2+ influx occurs in the cells of nervous systems. We found the capacitative Ca2+ influx in the neural retina of early embryonic chick with Fura-2 fluorescence measurements. A Ca(2+)-free medium containing thapsigargin (500 nM), an inhibitor of Ca(2+)-ATPase of intracellular Ca2+ stores, was applied to the neural retina of embryonic day 3 (E3) chick. A rise in intracellular Ca2+ concentration was evoked after the reintroduction of extracellular Ca2+, and this Ca2+ rise was suppressed by Zn2+ (1 mM) and Ni2+ (5 mM). The developmental changes in the Ca2+ rise induced by thapsigargin (250 nM) were studied from E3 to E13. The thapsigargin-induced Ca2+ rise was largest at E3, declined rapidly toward E6, and then decreased gradually until E13, when the Ca2+ rise almost disappeared. This developmental profile correlated with the decline in the mitotic activities of the retinal cells studied by Prada et al. The fluorescence imaging with the vertical slice of the E9 retina showed that the site at which the thapsigargin-induced Ca2+ rise was largest was the most outer layer of the retina, where proliferating cells are located. This spatial distribution and the above developmental profile may suggest that the capacitative Ca2+ influx occurs at the early period of neurogenesis when the cells have mitotic activities.

Agonist-releasable intracellular calcium stores and the phenomenon of store-dependent calcium entry. A novel hypothesis based on calcium stores in organelles of the endo- and exocytotic apparatus

Store-dependent calcium entry represents a little characterized calcium permeation pathway that is present in a variety of cell types. It is activated in an unknown way by depletion of intracellular calcium stores, for example in the course of phospholipase C stimulation. Current hypotheses propose that depleted calcium stores signal their filling state to this permeation pathway either by direct, protein-mediated interaction or by release of a small, diffusible messenger. The further characterization of store-dependent calcium entry will benefit from progress in the identification of the intracellular calcium storing compartments. Recent findings reviewed here suggest that these compartments include parts of the organelle system that is involved in endo- and exocytosis. This commentary describes a novel model of store-dependent calcium entry based on calcium stores belonging to the endo- and exocytotic organelle system. Such calcium stores could establish a tubule-like connection with the extracellular space, in analogy to the cellular compartments that contain the insulin-sensitive glucose transporter or the gastric proton pump. This connection will provide a pathway for store-dependent calcium entry. Under store depletion, extracellular calcium will permeate through the tubule-like connection into the store lumen and from there into the cytosol. The consequences of this model for the development of drugs modulating store-dependent calcium entry are discussed.

Simplification and analysis of models of calcium dynamics based on IP3-sensitive calcium channel kinetics

We study the models for calcium (Ca) dynamics developed in earlier studies, in each of which the key component is the kinetics of intracellular inositol-1,4,5-trisphosphate-sensitive Ca channels. After rapidly equilibrating steps are eliminated, the channel kinetics in these models are represented by a single differential equation that is linear in the state of the channel. In the reduced kinetic model, the graph of the steady-state fraction of conducting channels as a function of log10(Ca) is a bell-shaped curve. Dynamically, a step increase in inositol-1,4,5-trisphosphate induces an incremental increase in the fraction of conducting channels, whereas a step increase in Ca can either potentiate or inhibit channel activation, depending on the Ca level before and after the increase. The relationships among these models are discussed, and experimental tests to distinguish between them are given. Under certain conditions the models for intracellular calcium dynamics are reduced to the singular perturbed form epsilon dx/d tau = f(x, y, p), dy/d tau = g(x, y, p). Phase-plane analysis is applied to a generic form of these simplified models to show how different types of Ca response, such as excitability, oscillations, and a sustained elevation of Ca, can arise. The generic model can also be used to study frequency encoding of hormonal stimuli, to determine the conditions for stable traveling Ca waves, and to understand the effect of channel properties on the wave speed.

Pharmacologic characterization of refilling inositol 1,4,5-trisphosphate-sensitive Ca2+ stores in NG108-15 cells

Following mobilization with the inositol 1,4,5-trisphosphate (IP3)-generating agonist bradykinin, Ca2+ stores in neuroblastoma x glioma hybrid, NG108-15 cells require extracellular Ca2+ to refill. The process by which this store refills with Ca2+ was characterized by recording bradykinin-induced intracellular free Ca2+ concentration transients as an index of the degree of refilling of the store. Cyclopiazonic acid, a microsomal Ca2+ ATPase inhibitor, reversibly depleted intracellular Ca2+ stores in these cells, but did not recruit detectable Ca2+ influx, suggesting that these cells lack substantial capacitative Ca2+ entry. The paucity of voltage-sensitive Ca2+ channels in undifferentiated NG108-15 cells, suggested that a channel analogous to that proposed to mediate capacitative Ca2+ entry in nonexcitable cells might assist refilling IP3-sensitive Ca2+ stores in these cells. The possibility that compounds shown previously to inhibit capacitative Ca2+ entry in nonexcitable cells might inhibit the refilling of the IP3-sensitive store in NG108-15 cells was explored. The IP3-sensitive store was depleted by exposure to bradykinin, allowed to refill briefly in the presence of the test compound and then challenged again with bradykinin to evaluate the degree of refilling of the store. The imidazole derivatives, econazole (10 microM), L-651582 (10 microM) and SKF 96365 (20 microM), all completely blocked the bradykinin-induced Ca2+ response. Calmodulin antagonists, W-7 (100 microM) and trifluoperazine (10 microM), were also effective, although at concentrations well above those required to inhibit calmodulin. Because of the high concentrations required to inhibit bradykinin responses, the possibility that these agents might have additional effects was explored. Compounds were tested in a paradigm in which the store was preloaded with Ca2+ before treatment. All of these agents depleted, at least partially, the preloaded store. Econazole was the least effective of the compounds tested for releasing stores, although it was comparable to the other compounds for inhibition of refilling. Although NG108-15 cells refill intracellular Ca2+ stores by a plasmalemmal Ca2+ leak, this leak shares a pharmacology similar to the capacitative Ca2+ entry pathway described for nonexcitable cells.

H2O2 and tumor necrosis factor-alpha activate intercellular adhesion molecule 1 (ICAM-1) gene transcription through distinct cis-regulatory elements within the ICAM-1 promoter

We investigated the mechanisms by which H2O2 increases intercellular adhesion molecule 1 (ICAM-1; CD54) expression in endothelial cells. The H2O2-induced increase in ICAM-1 mRNA was inhibited by actinomycin D, by the antioxidant N-acetylcysteine, and by 3-amino-benzamide (which blocks oxidant-induced AP-1 activity), but not by pyrrolidine dithiocarbamate (which blocks oxidant-induced NF-kappa B activity). Nuclear run-on and transient transfections of ICAM-1 promoter constructs indicated that H2O2 stimulated ICAM-1 gene transcription by activation of a distinct region of the ICAM-1 promoter. The H2O2-responsive element was localized to sequences between -981 and -769 (relative to start codon). Located within this region are two 16-base pair repeats, each containing binding sites for the transcription factors AP-1 and Ets. A similar composite AP-1/Ets element isolated from the macrophage scavenger receptor gene conferred H2O2 responsiveness to a minimal promoter. Mutation of the 16-base pair repeats within the ICAM-1 promoter prevented H2O2-induced DNA binding activity, and their deletion abrogated the H2O2-induced transcriptional activity. In contrast, TNF alpha induced ICAM-1 transcription via activation of promoter sequences between -393 and -176, a region with C/EBP and NF-kappa B binding sites. The results indicate that H2O2 activates ICAM-1 transcription through AP-1/Ets elements within the ICAM-1 promoter, which are distinct from NF-kappa B-mediated ICAM-1 expression induced by TNF alpha.

Inositol trisphosphate receptor mediated spatiotemporal calcium signalling

Spatiotemporal Ca2+ signalling in the cytoplasm is currently understood as an excitation phenomenon by analogy with electrical excitation in the plasma membrane. In many cell types, Ca2+ waves and Ca2+ oscillations are mediated by inositol 1,4,5-trisphosphate (IP3) receptor/Ca2+ channels in the endoplasmic reticulum membrane, with positive feedback between cytosolic Ca2+ and IP3-induced Ca2+ release creating a regenerative process. Remarkable advances have been made in the past year in the analysis of subcellular Ca2+ microdomains using confocal microscopy and of Ca2+ influx pathways that are functionally coupled to IP3-induced Ca2+ release. Ca2+ signals can be conveyed into the nucleus and mitochondria. Ca2+ entry from outside the cell allows repetitive Ca2+ release by providing Ca2+ to refill the endoplasmic reticulum stores, thus giving rise to frequency-encoded Ca2+ signals.

Hydrogen peroxide as a potent activator of T lymphocyte functions

During inflammatory processes infiltrating cells produce large amounts of reactive oxygen intermediates (ROI). Increasing evidence suggests that ROI besides being cytotoxic may act as important mediators influencing various cellular and immunological processes. In this study, we have investigated the effects of hydrogen peroxide on several aspects of lymphocyte activation. In ESb-L T lymphoma cells, micromolar concentrations of hydrogen peroxide rapidly induced activation of the transcription factor NF-kappa B, whereas DNA-binding activity of the transcription factor AP-1 was virtually not affected. In addition, hydrogen peroxide induced early gene expression of interleukin-2 (IL-2) and the IL-2 receptor alpha chain. The stimulation of IL-2 expression was found to be conferred by a kappa B-like cis-regulatory region within the IL-2 gene promoter. In contrast to these activating effects, addition of hydrogen peroxide was largely inhibitory on cell proliferation which is consistent with a general requirement of thiol compounds for lymphocyte proliferation. However, hydrogen peroxide significantly increased T cell proliferation when applied for a short period under reducing conditions. These data indicate that ROI may act as an important competence signal in T lymphocytes inducing early gene expression as well as cell proliferation.

U73122 inhibits phospholipase C-dependent calcium mobilization in neuronal cells

The aminosteroid U73122 inhibited phospholipase C (PLC)-mediated intracellular Ca2+ release in differentiated and undifferentiated NG108-15 cells, as well as rat dorsal root ganglion (DRG) neurons grown in primary culture. 1 microM U73122 blocked bradykinin (BK)-induced increases in the intracellular free Ca2+ concentration ([Ca2+]i) measured in single cells with indo-1-based dual emission microfluorimetry. A close structural analog, U73343, was without effect. The effects of U73122 were time and concentration-dependent. 1 microM drug produced half maximal inhibition in approximately 3 min. The IC50 for a 20-min exposure was approximately 200 nM. The effects of the compound were irreversible for the duration of experiments as long as 1 h. Treatment with 1 microM U73122, but not U73343 produced a small but significant increase in [Ca2+]i which resulted from Ca2+ release from an intracellular store. It is not clear whether this [Ca2+]i increase resulted from inhibition of PLC or an action on the store directly. In differentiated NG108-15 cells U73122 blocked completely depolarization-induced Ca2+ influx. In contrast, in DRG neurons U73122 inhibited only slightly voltage-sensitive Ca2+ channels. Thus, we caution that U73122 may not be selective at concentrations required for maximal block of PLC and that the selectivity of U73122 is dependent on cell type. Overall, our results are consistent with U73122 inhibiting PLC in neuronal cells and indicate that under the appropriate conditions, this compound is a useful tool for studying inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ mobilization.

Meconium-induced lung injury mediated by activation of alveolar macrophages

To clarify the mechanism of meconium-induced cellular injury, we examined the effect of meconium on the alveolar macrophages (AM) and bronchial epithelial cells (AK-D). Meconium obtained from healthy newborns was added to culture medium of AM and/or AK-D, which were cultured for 1 hour. Superoxide anion production of AM and the expression of intercellular adhesion molecule-1 (ICAM-1) on AK-D stimulated by meconium or oxygen radicals were determined. As a result, superoxide anion production of AM significantly increased when AM was cultured with meconium. Expression of ICAM-1 on AK-D appeared when AK-D was stimulated by hydroxyl radical but did not when AK-D was cultured with meconium. These results suggest that meconium-induced lung injury may occur through an activation of alveolar macrophages and the macrophage-epithelial cell axis may be important for the pathogenesis of meconium aspiration syndrome.