Inhibitory Effect of Fulvic Acid Extracted from Canadian Sphagnum Peat on Chemical Mediator Release by RBL-2H3 and KU812 Cells

Fulvic acid (FA) was extracted and purified from Canadian Sphagnum peat (CP-FA) and characterized by using an element analysis meter, Fourier transform infrared (FT-IR) spectroscopy, electron spin resonance (ESR) spectroscopy, and ¹³C-nuclear magnetic resonance (¹³C-NMR) spectroscopy. To investigate the antiallergic effect of CP-FA, we incubated rat basophilic leukemia (RBL-2H3) cells with 0.001–10.0 μg/ml of CP-FA and determined the β-hexosaminidase release inhibition at different response stages. The intracellular calcium [Ca²⁺] _i level was also determined by using Fluo 3-AM, a calcium-specific fluorescent probe, and the cytotoxicity of CP-FA was determined by the 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. The results revealed that RBL-2H3 cells incubated for 48 h with 0.001–10.0 μg/ml of CP-FA did not show any decreased viability. CP-FA inhibited the β-hexosaminidase release by IgE-sensitized, antigen-stimulated RBL-2H3 cells at the antigen-antibody binding stage and the antibody-receptor binding stage. CP-FA also inhibited histamine release from A23187 plus PMA- or compound 48/80-stimulated KU812 cells. Furthermore, there was a decrease in the intracellular [Ca²⁺] _i level in IgE-sensitized cells incubated with CP-FA and stimulated with antigen. Our results show that CP-FA may be useful for the treatment or prevention of allergic diseases.     

Inhibitory effect of xanthones isolated from the pericarp of Garcinia mangostana L. on rat basophilic leukemia RBL-2H3 cell degranulation

Mangostin, Garcinia mangostana L. is used as a traditional medicine in southeast Asia for inflammatory and septic ailments. Hitherto we indicated the anticancer activity induced by xanthones such as alpha-, beta-, and gamma-mangostin which were major constituents of the pericarp of mangosteen fruits. In this study, we examined the effect of xanthones on cell degranulation in rat basophilic leukemia RBL-2H3 cells. Antigen (Ag)-mediated stimulation of high affinity IgE receptor (FcepsilonRI) activates intracellular signal transductions resulting in the release of biologically active mediators such as histamine. The release of histamine and other inflammatory mediators from mast cell or basophils is the primary event in several allergic responses. These xanthones suppressed the release of histamine from IgE-sensitized RBL-2H3 cells. In order to reveal the inhibitory mechanism of degranulation by xanthones, we examined the activation of intracellular signaling molecules such as Lyn, Syk, and PLCgammas. All the xanthones tested significantly suppressed the signaling involving Syk and PLCgammas. In Ag-mediated activation of FcepsilonRI on mast cells, three major subfamilies of mitogen-activated protein kinases were activated. The xanthones decreased the level of phospho-ERKs. Furthermore, the levels of phospho-ERKs were observed to be regulated by Syk/LAT/Ras/ERK pathway rather than PKC/Raf/ERK pathway, suggesting that the inhibitory mechanism of xanthones was mainly due to suppression of the Syk/PLCgammas/PKC pathway. Although intracellular free Ca(2+) concentration ([Ca(2+)](i)) was elevated by FcepsilonRI activation, it was found that alpha- or gamma-mangostin treatment was reduced the [Ca(2+)](i) elevation by suppressed Ca(2+) influx.     

Degranulation in RBL-2H3 cells: regulation by calmodulin pathway

Involvement of the calmodulin pathway in Ca2+-induced degranulation was evaluated in RBL-2H3 mast cells. Pretreatment of RBL-2H3 cells with a calmodulin antagonist, W-13, blocked ionomycin-dependent release of beta-hexosaminidase into the supernatant, although W-13 treatment alone slightly but significantly increased the release. Ca2+/calmodulin activates various protein kinases and phosphatases including myosin-light chain kinase (MLCK), calmodulin-dependent protein kinases (CaMKs), and calcineurin. When RBL-2H3 cells were pretreated with a MLCK inhibitor, ML-7, or a CaMKs inhibitor, KN-93, the ionomycin-dependent release of beta-hexosaminidase into the supernatant was inhibited. In addition, pretreatment with calcineurin inhibitors, cyclosporin A and FR901725, resulted in blockage of the ionomycin-dependent release of beta-hexosaminidase into the supernatant. Our results indicate that Ca2+/calmodulin, activated calmodulin, is indispensable for Ca2+-induced degranulation, and that within the calmodulin pathways, at least MLCK, CaMKs and calcineurin positively regulate the release of granules initiated by increasing cytosolic Ca2+ concentrations in RBL-2H3 cells.     

Na(+)-dependent Ca(2+) transport modulates the secretory response to the Fcepsilon receptor stimulus of mast cells

Immunological stimulation of rat mucosal-type mast cells (RBL-2H3 line) by clustering of their Fcepsilon receptors (FcepsilonRI) causes a rapid and transient increase in free cytoplasmic Ca(2+) ion concentration ([Ca(2+)](i)) because of its release from intracellular stores. This is followed by a sustained elevated [Ca(2+)](i), which is attained by Ca(2+) influx. Because an FcepsilonRI-induced increase in the membrane permeability for Na(+) ions has also been observed, and secretion is at least partially inhibited by lowering of extracellular sodium ion concentrations ([Na(+)](o)), the operation of a Na(+)/Ca(2+) exchanger has been considered. We found significant coupling between the Ca(2+) and Na(+) ion gradients across plasma membranes of RBL-2H3 cells, which we investigated employing (23)Na-NMR, (45)Ca(2+), (85)Sr(2+), and the Ca(2+)-sensitive fluorescent probe indo-1. The reduction in extracellular Ca(2+) concentrations ([Ca(2+)](o)) provoked a [Na(+)](i) increase, and a decrease in [Na(+)](o) results in a Ca(2+) influx as well as an increase in [Ca(2+)](i). Mediator secretion assays, monitoring the released beta-hexosaminidase activity, showed in the presence of extracellular sodium a sigmoidal dependence on [Ca(2+)](o). However, the secretion was not affected by varying [Ca(2+)](o) as [Na(+)](o) was lowered to 0.4 mM, while it was almost completely inhibited at [Na(+)](o) = 136 mM and [Ca(2+)](o) < 0.05 mM. Increasing [Na(+)](o) caused the secretion to reach a minimum at [Na(+)](o) = 20 mM, followed by a steady increase to its maximum value at 136 mM. A parallel [Na(+)](o) dependence of the Ca(2+) fluxes was observed: Antigen stimulation at [Na(+)](o) = 136 mM caused a pronounced Ca(2+) influx. At [Na(+)](o) = 17 mM only a slight Ca(2+) efflux was detected, whereas at [Na(+)](o) = 0.4 mM no Ca(2+) transport across the cell membrane could be observed. Our results clearly indicate that the [Na(+)](o) dependence of the secretory response to FcepsilonRI stimulation is due to its influence on the [Ca(2+)](i), which is mediated by a Na(+)-dependent Ca(2+) transport.     

Anti-allergic activity of stilbenes from Korean rhubarb (Rheum undulatum L.): structure requirements for inhibition of antigen-induced degranulation and their effects on the release of TNF-alpha and IL-4 in RBL-2H3 cells

Stilbenes isolated from the rhizomes of Rheum undulatum (Korean rhubarb) and the related compounds were investigated on their anti-allergic activities. The results revealed that 3,5,4'-trimethylpiceatannol exhibited the most potent inhibition against beta-hexosaminidase release as a marker of degranulation in RBL-2H3 cells with IC(50) of 2.1 microM, followed by trimethylresveratrol (IC(50)=5.1 microM). Structural requirements of stilbenes for the activity are as follows: (1) The oxygen functions (-OCH(3), -OH), especially methoxyl groups, are essential and their positions on aromatic rings are important for the activity; (2) the alpha-beta double bond increased the activity; (3) the glycoside moiety dramatically decreased the activity; and (4) the substitution group at the 3'-position in trimethylresveratrol (3,5,4'-trimethoxystilbene) was preferably OH>H>OCH(3) for the activity. Several active stilbenes (piceatannol, 3,5,4'-trimethylpiceatannol, resveratrol, trimethylresveratrol) also inhibited ionomycin-induced beta-hexosaminidase release, suggesting that inhibition of Ca(2+) influx or degranulation mechanisms after Ca(2+) influx is important for their activities. Piceatannol, 3,5,4'-trimethylpiceatannol, resveratrol, and trimethylresveratrol also significantly inhibited antigen-induced release of TNF-alpha and IL-4 in RBL-2H3 cells.     

Roles for Ca2+ stores release and two Ca2+ influx pathways in the Fc epsilon R1-activated Ca2+ responses of RBL-2H3 mast cells.

Cross-linking the high affinity IgE receptor, Fc epsilon R1, with multivalent antigen induces inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]-dependent release of intracellular Ca2+ stores, Ca2+ influx, and secretion of inflammatory mediators from RBL-2H3 mast cells. Here, fluorescence ratio imaging microscopy was used to characterize the antigen-induced Ca2+ responses of single fura-2-loaded RBL-2H3 cells in the presence and absence of extracellular Ca2+ (Ca2+o). As antigen concentration increases toward the optimum for secretion, more cells show a Ca2+ spike or an abrupt increase in [Ca2+]i and the lag time to onset of the response decreases both in the presence and the absence of Ca2+o. When Ca2+o is absent, fewer cells respond to low antigen and the lag times to response are longer than those measured in the presence of Ca2+o, indicating that Ca2+o contributes to Ca2+ stores release. Ins(1,4,5)P3 production is not impaired by the removal of Ca2+o, suggesting that extracellular Ca2+ influences Ca2+ stores release via an effect on the Ins(1,4,5)P3 receptor. Stimulation with low concentrations of antigen can lead, only in the presence of Ca2+o, to a small, gradual increase in [Ca2+]i before the abrupt spike response that indicates store release. We propose that this small, initial [Ca2+]i increase is due to receptor-activated Ca2+ influx that precedes and may facilitate Ca2+ stores release. A mechanism for capacitative Ca2+ entry also exists in RBL-2H3 cells. Our data suggest that a previously undescribed response to Fc epsilon R1 cross-linking, inhibition of Ca2+ stores refilling, may be involved in activating capacitative Ca2+ entry in antigen-stimulated RBL-2H3 cells, thus providing the elevated [Ca2+]i required for optimal secretion. The existence of both capacitative entry and Ca2+ influx that can precede Ca2+ release from intracellular stores suggests that at least two mechanisms of stimulated Ca2+ influx are present in RBL-2H3 cells.     

Characterization of a new type of variant of rat basophilic leukemia 2H3 cells presenting a different pattern of calcium signal

We selected a new type of variant (designated 3C7) derived spontaneously from parental RBL-2H3 cells. 3C7 cells showed lower contact inhibition, anchorage dependency, and serotonin release activity than those of RBL-2H3 cells. We conclude that 3C7 cells are a transformant of RBL-2H3 cell with greater malignancy. The production of inositol bisphosphate and the release of Ca2+ from intracellular stores induced by IgE-antigen stimulation were enhanced in 3C7. Oscillation of [Ca2+]i in individual 3C7 cells was observed by a digital imaging microscopic technique. We propose that 3C7 cells are a useful model system for studies on the mechanisms of stimulus-secretion coupling and the relationships between malignant alterations and disorders of signal transduction.     

Developmental changes in capacitative Ca(2+) entry in mouse mammary epithelial cells

Developmental changes in capacitative Ca(2+) entry and Ca(2+) release from intracellular stores were measured using fura-2 fluorescence method during the pregnancy period (day 3-;18) in mouse mammary epithelial cells. Ca(2+) release was identified with the transient intracellular Ca(2+) ([Ca(2+)](i)) increase induced by thapsigargin addition in a Ca(2+)-free solution. Capacitative Ca(2+) entry was measured by the transient [Ca(2+)](i) increase induced by re-addition of extracellular Ca(2+) after depletion of Ca(2+) stores by thapsigargin. The capacitative Ca(2+) entry was greatest at the early stage of pregnancy (i.e. day 3 of pregnancy) and decreased as pregnancy progressed, while Ca(2+) release remained unchanged throughout the developmental stages. These findings indicate that in contrast to Ca(2+) release, a close correlation exists between capacitative Ca(2+) entry and pregnancy-induced development in mammary epithelial cells.     

Bacterial lipopolysaccharide activates protein kinase C, but not intracellular calcium elevation, in human peripheral T cells

The increase of intracellular free calcium concentration ([Ca(2+)](i)) and protein kinase C (PKC) activity are two major early mitogenic signals to initiate proliferation of human peripheral T cells. Bacterial lipopolysaccharide (LPS) is nonmitogenic in human T cells. However, in the presence of monocytes, LPS becomes mitogenic to proliferate T cells. The aim of this study was to define the incompetency of LPS on two mitogenic signals in human peripheral T cells. T cells were isolated from human peripheral blood. [Ca(2+)](i) and pH(i) were determined by loading the cells with the fluorescent dyes, Fura-2 acetoxymethyl ester (Fura-2/AM) and 2',7'-bis(2-carboxyethyl)-5-(and 6)carboxyfluorescein acetoxymethyl ester (BCECF/AM). PKC activity was determined by protein kinase assay and cell proliferation was estimated from the incorporation of [(3)H]-thymidine. The results indicated that (1) LPS (10 microg/ml) stimulated PKC activity significantly within 5 min, reached a plateau at 30 min, and maintained that level for at least 2 h; and (2) LPS stimulated cytoplasmic alkalinization but did not affect the levels of [Ca(2+)](i) and [(3)H]-thymidine incorporation into T cells. Moreover, the combination of calcium ionophore A23187 with LPS significantly stimulated [(3)H]-thymidine incorporation into T cells. Thus, the results demonstrate that LPS failed to proliferate T cells, probably because of a lack of the machinery necessary to stimulate the mitogenic signal on [Ca(2+)](i) elevation.     

Mobilization of intracellular Ca(2+) by endothelin-1 in rat intrapulmonary arterial smooth muscle cells

Endothelin-1 (ET-1) increases intracellular Ca(2+) concentration ([Ca(2+)](i)) in pulmonary arterial smooth muscle cells (PASMCs); however, the mechanisms for Ca(2+) mobilization are not clear. We determined the contributions of extracellular influx and intracellular release to the ET-1-induced Ca(2+) response using Indo 1 fluorescence and electrophysiological techniques. Application of ET-1 (10(-10) to 10(-8) M) to transiently (24-48 h) cultured rat PASMCs caused concentration-dependent increases in [Ca(2+)](i). At 10(-8) M, ET-1 caused a large, transient increase in [Ca(2+)](i) (>1 microM) followed by a sustained elevation in [Ca(2+)](i) (<200 nM). The ET-1-induced increase in [Ca(2+)](i) was attenuated (<80%) by extracellular Ca(2+) removal; by verapamil, a voltage-gated Ca(2+)-channel antagonist; and by ryanodine, an inhibitor of Ca(2+) release from caffeine-sensitive stores. Depleting intracellular stores with thapsigargin abolished the peak in [Ca(2+)](i), but the sustained phase was unaffected. Simultaneously measuring membrane potential and [Ca(2+)](i) indicated that depolarization preceded the rise in [Ca(2+)](i). These results suggest that ET-1 initiates depolarization in PASMCs, leading to Ca(2+) influx through voltage-gated Ca(2+) channels and Ca(2+) release from ryanodine- and inositol 1,4,5-trisphosphate-sensitive stores.     

Polyphosphate Is a Novel Pro-inflammatory Regulator of Mast Cells and Is Located in Acidocalcisomes

Polyphosphate (polyP) is a pro-inflammatory agent and a potent modulator of the human blood-clotting system. The presence of polyP of 60 phosphate units was identified in rat basophilic leukemia (RBL-2H3) mast cells using specific enzymatic assays, urea-polyacrylamide gel electrophoresis of cell extracts, and staining of cells with 4,6-diamidino-2-phenylindole (DAPI), and the polyP-binding domain of Escherichia coli exopolyphosphatase. PolyP co-localizes with serotonin- but not with histamine-containing granules. PolyP levels greatly decreased in mast cells stimulated to degranulate by IgE. Mast cell granules were isolated and found to be acidic and decrease their polyP content upon alkalinization. In agreement with these results, when RBL-2H3 mast cells were loaded with the fluorescent calcium indicator fura-2 acetoxymethyl ester to measure their intracellular Ca(2+) concentration ([Ca(2+)](i)), they were shown to possess a significant amount of Ca(2+) stored in an acidic compartment different from lysosomes. PolyP derived from RBL-2H3 mast cells stimulated bradykinin formation, and it was also detected in human basophils. All of these characteristics of mast cell granules, together with their known elemental composition, and high density, are similar to those of acidocalcisomes. The results suggest that mast cells polyP could be an important mediator of their pro-inflammatory and pro-coagulant activities.     

The Effects of Low-dose Ionizing Radiation in the Activated Rat Basophilic Leukemia (RBL-2H3) Mast Cells

Mast cells play important roles in many biological responses, such as those during allergic diseases and inflammatory disorders. Although laser and UV irradiation have immunosuppressive effects on inflammatory diseases by suppressing mast cells, little is known about the effects of γ-ionizing radiation on mast cells. In this study, we investigated the effects of γ-ionizing radiation on RBL-2H3 cells, a convenient model system for studying regulated secretion by mast cells. Low-dose radiation (<0.1 gray (Gy)) did not induce cell death, but high-dose radiation (>0.5 Gy) induced apoptosis. Low-dose ionizing radiation significantly suppressed the release of mediators (histamine, β-hexosaminidase, IL-4, and tumor necrosis factor-α) from immunoglobulin E (IgE)-sensitized RBL-2H3 cells. To determine the mechanism of mediator release inhibition by ionizing radiation, we examined the activation of intracellular signaling molecules such as Lyn, Syk, phospholipase Cγ, PKCs, and MAPK, and intracellular free calcium concentrations ([Ca(2+)](i)). The phosphorylation of signaling molecules following stimulation of high-affinity IgE receptor I (FcεRI) was specifically inhibited by low-dose ionizing radiation (0.01 Gy). These results were due to the suppression of FcεRI expression by the low-dose ionizing radiation. Therefore, low-dose ionizing radiation (0.01 Gy) may function as a novel inhibitor of mast cell activation.     

Effect of hydrogen peroxide and superoxide anions on cytosolic Ca2+: comparison of endothelial cells from large-sized and small-sized arteries

We compared the Ca(2+) responses to reactive oxygen species (ROS) between mouse endothelial cells derived from large-sized arteries, aortas (aortic ECs), and small-sized arteries, mesenteric arteries (MAECs). Application of hydrogen peroxide (H(2)O(2)) caused an increase in cytosolic Ca(2+) levels ([Ca(2+)](i)) in both cell types. The [Ca(2+)](i) rises diminished in the presence of U73122, a phospholipase C inhibitor, or Xestospongin C (XeC), an inhibitor for inositol-1,4,5-trisphosphate (IP(3)) receptors. Removal of Ca(2+) from the bath also decreased the [Ca(2+)](i) rises in response to H(2)O(2). In addition, treatment of endothelial cells with H(2)O(2) reduced the [Ca(2+)](i) responses to subsequent challenge of ATP. The decreased [Ca(2+)](i) responses to ATP were resulted from a pre-depletion of intracellular Ca(2+) stores by H(2)O(2). Interestingly, we also found that Ca(2+) store depletion was more sensitive to H(2)O(2) treatment in endothelial cells of mesenteric arteries than those of aortas. Hypoxanthine-xanthine oxidase (HX-XO) was also found to induce [Ca(2+)](i) rises in both types of endothelial cells, the effect of which was mediated by superoxide anions and H(2)O(2) but not by hydroxyl radical. H(2)O(2) contribution in HX-XO-induced [Ca(2+)](i) rises were more significant in endothelial cells from mesenteric arteries than those from aortas. In summary, H(2)O(2) could induce store Ca(2+) release via phospholipase C-IP(3) pathway in endothelial cells. Resultant emptying of intracellular Ca(2+) stores contributed to the reduced [Ca(2+)](i) responses to subsequent ATP challenge. The [Ca(2+)](i) responses were more sensitive to H(2)O(2) in endothelial cells of small-sized arteries than those of large-sized arteries.     

Involvement of farnesyl protein transferase (FPTase) in FcarepsilonRI-induced activation of RBL-2H3 mast cells

Changes in farnesyl protein transferase (FPTase) activity and FPTase beta-subunit protein levels were determined in IgE-sensitized RBL-2H3 mast cells in response to polyvalent antigen administration. Ten minutes after the addition of DNP modified BSA to mast cells, whose high affinity receptor for IgE (FcvarepsilonRI) contained bound anti-DNP IgE, FPTase specific activity increased by 54 +/- 28%. Time course studies showed FPTase specific activity doubled during a 20- to 30-min period after antigen-induced cell aggregation. Also, an increase in FPTase beta-subunit protein during this time ( approximately 30%) was observed; this protein increase was not accompanied by a similar increase in FPTase beta-subunit m-RNA levels. The FcvarepsilonRI aggregation had no significant effect on the activities of other enzymes involved with farnesyl diphosphate (FPP) metabolism: FPP synthase, isopentenyl diphosphate isomerase, geranylgeranyl protein transferase, and squalene synthase. Specific inhibition of FPTase activity by manumycin was studied to determine what role FPTase plays in mast cell activation. Manumycin profoundly inhibited hexosaminidase release in activated cells, indicating FPTase is required for signal transduction involved with protein exocytosis from RBL-2H3 mast cells.     

Mobilization of intracellular calcium by peroxynitrite in arteriolar smooth muscle cells from rats

The present study was designed to investigate the possible effects of peroxynitrite (ONOO(-)) on the intracellular calcium concentration ([Ca(2+)](i)) of mesenteric arteriolar smooth muscle cells (ASMCs), and to reveal the underlying mechanisms by using fluorescence imaging analysis. The results showed that ONOO(-) could exert a concentration- and time-dependent but also a dual effect on [Ca(2+)](i). Bolus administration with a low concentration of ONOO(-) (25 microM) decreased [Ca(2+)](i), whereas higher concentrations (50 or 100 microM) increased [Ca(2+)](i) persistently. Further experiments demonstrated that pretreatment of ASMCs with calcium-free medium completely abolished [Ca(2+)](i) increase by 100 microM ONOO(-). Additionally, nifedipine, an antagonist of selective L-type voltage-gated calcium channels (VGCCs), delayed the [Ca(2+)](i) response to ONOO(-), and ryanodine, an inhibitor of intracellular calcium release from the sarcoplasmic reticulum, effectively antagonized [Ca(2+)](i) increase during the late stage of ONOO(-) exposure. Furthermore, [Ca(2+)](i) alteration by ONOO(-) appeared to be intimately associated with the subsequent membrane potential changes. Although the mechanisms by which ONOO(-) alters [Ca(2+)](i) are complex, we conclude that a series of variables such as external calcium influx, activation of VGCCs, intracellular calcium release, and membrane potential changes are involved. The decrease of [Ca(2+)](i) in ASMCs by a low concentration of ONOO(-) may participate in the pathogenesis of low vasoreactivity in shock, and the increase of [Ca(2+)](i) by high concentrations of ONOO(-) may lead to calcium overload with cellular injury.     

Ca(2+)](i) signaling in renal arterial smooth muscle cells of pregnant rat is enhanced during inhibition of NOS

Vascular resistance and arterial pressure are reduced during normal pregnancy, but dangerously elevated during pregnancy-induced hypertension (PIH), and changes in nitric oxide (NO) synthesis have been hypothesized as one potential cause. In support of this hypothesis, chronic inhibition of NO synthesis in pregnant rats has been shown to cause significant increases in renal vascular resistance and hypertension; however, the cellular mechanisms involved are unclear. We tested the hypothesis that the pregnancy-associated changes in renal vascular resistance reflect changes in contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) of renal arterial smooth muscle. Smooth muscle cells were isolated from renal interlobular arteries of virgin and pregnant Sprague-Dawley rats untreated or treated with the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME; 4 mg. kg(-1). day(-1) for 5 days), then loaded with fura 2. In cells of virgin rats incubated in Hanks' solution (1 mM Ca(2+)), the basal [Ca(2+)](i) was 86 +/- 6 nM. Phenylephrine (Phe, 10(-5) M) caused a transient increase in [Ca(2+)](i) to 417 +/- 11 nM and maintained an increase to 183 +/- 8 nM and 32 +/- 3% cell contraction. Membrane depolarization by 51 mM KCl, which stimulates Ca(2+) entry from the extracellular space, caused maintained increase in [Ca(2+)](i) to 292 +/- 12 nM and 31 +/- 2% contraction. The maintained Phe- and KCl-induced [Ca(2+)](i) and contractions were reduced in pregnant rats but significantly enhanced in pregnant rats treated with L-NAME. Phe- and KCl-induced contraction and [Ca(2+)](i) were not significantly different between untreated and L-NAME-treated virgin rats or between untreated and L-NAME + L-arginine treated pregnant rats. In Ca(2+)-free Hanks', application of Phe or caffeine (10 mM), to stimulate Ca(2+) release from the intracellular stores, caused a transient increase in [Ca(2+)](i) and a small cell contraction that were not significantly different among the different groups. Thus renal interlobular smooth muscle of normal pregnant rats exhibits reduction in [Ca(2+)](i) signaling that involves Ca(2+) entry from the extracellular space but not Ca(2+) release from the intracellular stores. The reduced renal smooth muscle cell contraction and [Ca(2+)](i) in pregnant rats may explain the decreased renal vascular resistance associated with normal pregnancy, whereas the enhanced cell contraction and [Ca(2+)](i) during inhibition of NO synthesis in pregnant rats may, in part, explain the increased renal vascular resistance associated with PIH.     

In vitro and in vivo anti-allergic effects of Arctium lappa L

The discovery of drugs that can be used for the treatment of allergic disease is important in human health. Arctium lappa Linne (Compositae) (AL) has been used as a traditional medicine in Brazil and throughout Asia and is known to have an anti-inflammatory effect. In this study, the inhibitory effects of AL on degranulation and the release of mediators as well as on inhibition of cys-leukotriene biosynthesis by basophils were investigated. AL was selected out of 10,000 herbal extracts in a set-up for high throughput screening in which the degree of degranulation was monitored by the release of beta-hexosaminidase from rat basophil leukemia (RBL-2H3) cells. The AL extract significantly reduced degranulation and biosynthesis of cys-leukotrienes of human basophils in peripheral blood mono-nuclear cells (PBMCs) (50% inhibitory concentration [IC(50)] = 8.3 and 11.4 microg/ml, respectively). Viability and metabolic activity of the PBMCs were not affected. Although arctiin, the active component of AL that has been described in the literature, was not able to reduce degranulation in RBL-2H3 cells, a single high-performance liquid chromatography (HPLC) fraction from the AL extract inhibited beta-hexosaminidase release (IC(50) = 22.2 microg/ml). Topical administration of an aqueous extract of AL (5 mg/ear) on the ear of whey-sensitized mice 4 hrs before challenge with whey in the ear inhibited acute ear swelling by 50% in an in vivo cow's milk allergic model. The extract had no effect in this model when administered orally. In conclusion, the active component present in the active HPLC fraction of the AL extract was able to significantly reduce the release of inflammatory mediators through inhibition of degranulation and cys-leukotriene release in vitro. In addition, this active component was able to inhibit acute skin response in mice in vivo, indicating that AL is a very promising natural component for use in anti-allergic treatment.     

Effects of cigarette smoke on degranulation and NO production by mast cells and epithelial cells

Exhaled nitric oxide (eNO) is decreased by cigarette smoking. The hypothesis that oxides of nitrogen (NO_X) in cigarette smoke solution (CSS) may exert a negative feedback mechanism upon NO release from epithelial (AEC, A549, and NHTBE) and basophilic cells (RBL-2H3) was tested in vitro. CSS inhibited both NO production and degranulation (measured as release of beta-hexosaminidase) in a dose-dependent manner from RBL-2H3 cells. Inhibition of NO production by CSS in AEC, A549, and NHTBE cells was also dose-dependent. In addition, CSS decreased expression of NOS mRNA and protein expression. The addition of NO inhibitors and scavengers did not, however, reverse the effects of CSS, nor did a NO donor (SNP) or nicotine mimic CSS. N-acetyl-cysteine, partially reversed the inhibition of beta-hexosaminidase release suggesting CSS may act via oxidative free radicals. Thus, some of the inhibitory effects of CSS appear to be via oxidative free radicals rather than a NO_X -related negative feedback.     

Intracellular Ca(2+) signaling in endothelial cells by the angiogenesis inhibitors endostatin and angiostatin

Intracellular signaling mechanisms by the angiogenesis inhibitors endostatin and angiostatin remain poorly understood. We have found that endostatin (2 microg/ml) and angiostatin (5 microg/ml) elicited transient, approximately threefold increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). Acute exposure to angiostatin or endostatin nearly abolished subsequent endothelial [Ca(2+)](i) responses to carbachol or to thapsigargin; conversely, thapsigargin attenuated the Ca(2+) signal elicited by endostatin. The phospholipase C inhibitor U-73122 and the inositol trisphosphate (IP(3)) receptor inhibitor xestospongin C both inhibited endostatin-induced elevation in [Ca(2+)](i), and endostatin rapidly elevated endothelial cell IP(3) levels. Pertussis toxin and SB-220025 modestly inhibited the endostatin-induced Ca(2+) signal. Removal of extracellular Ca(2+) inhibited the endostatin-induced rise in [Ca(2+)](i), as did a subset of Ca(2+)-entry inhibitors. Peak Ca(2+) responses to endostatin and angiostatin in endothelial cells exceeded those in epithelial cells and were minimal in NIH/3T3 cells. Overnight pretreatment of endothelial cells with endostatin reduced the subsequent acute elevation in [Ca(2+)](i) in response to vascular endothelial growth factor or to fibroblast growth factor by approximately 70%. Intracellular Ca(2+) signaling may initiate or mediate some of the cellular actions of endostatin and angiostatin.     

Low cytoplasmic [Ca(2+)] activates I(CRAC) independently of global Ca(2+) store depletion in RBL-1 cells

Release of Ca(2+) from inositol (1,4,5)-trisphosphate-sensitive Ca(2+) stores causes "capacitative calcium entry," which is mediated by the so-called "Ca(2+) release-activated Ca(2+) current" (I(CRAC)) in RBL-1 cells. Refilling of the Ca(2+) stores or high cytoplasmic [Ca(2+)] ([Ca(2+)](cyt)) inactivate I(CRAC). Here we address the question if also [Ca(2+)](cyt) lower than the resting [Ca(2+)](cyt) influences store-operated channels. We therefore combined patch clamp and mag fura-2 fluorescence methods to determine simultaneously both I(CRAC) and [Ca(2+)] within Ca(2+) stores of RBL-1 cells ([Ca(2+)](store)). We found that low [Ca(2+)](cyt) in the range of 30-50 nM activates I(CRAC) and Ca(2+) influx spontaneously and independently of global Ca(2+) store depletion, while elevation of [Ca(2+)](cyt) to the resting [Ca(2+)](cyt) (100 nM) resulted in store dependence of I(CRAC) activation. We conclude that spontaneous activation of I(CRAC) by low [Ca(2+)](cyt) could serve as a feedback mechanism keeping the resting [Ca(2+)](cyt) constant.