Showing papers on "Vanadate published in 1997"
TL;DR: The results show that vanadate is a competitive inhibitor for the protein-tyrosine phosphatase PTP1B, with a Ki of 0.38 ± 0.02 μM, and reducing agents such as dithiothreitol that are used in PTP assays to keep the catalytic cysteine reduced and active were found to convert pervanadate rapidly toVanadate.
801 citations
TL;DR: It is suggested that nitric oxide is the putative elongation inducer and that IAA and NO·–releasing substances conceivably share common steps in the signal transduction pathway, since both elicited the same plant response.
Abstract: Root segments of maize were incubated in different solutions containing substances that non-enzymatically release nitric oxide, such as sodium nitrite (SN), sodium nitroprusside (SNP), nitrosoglutathione (NGLU) and nitrosocysteine (NCYS). We found that all of these substances induced root tip expansion in a dose-dependent manner. The decreasing order of potency for root-induced elongation was: 10 -7 M SN, pH 4.5; 10 -11 M NCYS, 10 -10 M SNP, 10 -9 M NGLU and 10 -7 M SN, pH 7.0. Nitric oxide scavenger such as methylene blue prevented the elongation induced by NO·–releasing substances, but had no effect on indole-3-acetic acid (IAA)-induced cell expansion. Our results suggest that nitric oxide is the putative elongation inducer and that IAA and NO·–releasing substances conceivably share common steps in the signal transduction pathway, since both elicited the same plant response. Vanadate, a plasmamembrane ATPase inhibitor, significantly reversed IAA-induced elongation when supplied at 10 μM concentration. IAA-induced elongation was strongly enhanced by 10 nM BAY K 8644, an agonist of voltage dependent Ca2+ channels. Promotion of root elongation in the absence of IAA occurred only at higher concentrations of BAY K. Vanadate and BAY K had no influence on the NCYS-induced elongation suggesting that the common steps in the signalling of IAA and NCYS are not at the level of the plasmamembrane.
222 citations
TL;DR: Two studies are consistent with the conclusion that vanadate inhibits tyrosine phosphatases by acting as a transition state analog, and the structure of theVanadate complex may be expected to closely resemble the transition state for reactions catalyzed by protein tyrosining phosphatase enzymes.
Abstract: The early transition metal oxoanions vanadate, molybdate, and tungstate are widely used inhibitors for phosphatase enzymes. These oxoanions could inhibit such enzymes by simply mimicking the tetrah...
191 citations
TL;DR: A role for oxidative stress in the biological effects of some PTP inhibitors, whereas NF-κB activation by PTP inhibitor is mediated by mechanisms independent of intracellular redox status.
139 citations
TL;DR: It is demonstrated that vanadate‐induced trapping of 8‐azido‐ATP in MRP was stimulated in the presence of glutathione, oxidized glutathion and the anti‐cancer drugs VP‐16 and vincristine, and suggested that a stable inhibitory complex MRP·MgADP·Vi, an analog of the MRP ·Mg ADP·Pi transition state complex, is formed in the absence of vanadates.
114 citations
TL;DR: Results show that TM6 and TM12 undergo different conformational changes upon drug binding or during ATP hydrolysis, and that movement between these two helices is essential for drug-stimulated ATPase activity.
108 citations
TL;DR: The decrease in electrophoretic mobility and activation of PKB induced by insulin was reversed both in vitro by treatment of the enzyme with alkaline phosphatase and in the intact adipocyte upon removal of insulin or addition of the phosphatidylinositol 3-kinase (PI 3-Kinase) inhibitor wortmannin, suggesting that PI 3- Kinase and/or the 3-phosphorylated phosphoinositides generated by PI 3
78 citations
TL;DR: The data are consistent with the interpretation that vanadium oxalate and citrate complexes hydrolyze to vanadate, and would appear to be toxic for normal MC3T3E1 osteoblasts.
67 citations
TL;DR: All of the vanadate and vanadyl compounds tested in this study showed potent antibacterial activity against Streptococcus pneumoniae: the MIC (minimum inhibitory concentration) values of theVanadium compounds were 4-32 micrograms/ml, while the MIC values of tungstates and molybdates were 128-->8000 microgramS/ml.
Abstract: All of the vanadate and vanadyl compounds tested in this study showed potent antibacterial activity against Streptococcus pneumoniae: the MIC (minimum inhibitory concentration) values of the vanadium compounds were 4-32 micrograms/ml, while the MIC values of tungstates and molybdates were 128-->8000 micrograms/ml. Scanning electron microscopy showed the elongation of S. pneumoniae strains under low concentrations (< MIC) of vanadium compounds such as (tert-BuNH3)4[V4O12] (1), (tert-BuNH3)6[V10O28] (2), Na3VO4 (7) and VOSO4 (8). The vanadium compounds non-selectively inhibited the incorporation of thymidine, uridine, leucine and glucose into the cells of S. pneumoniae and led to an efflux of potassium ions from the cells. It implies that the vanadium compounds interfere in or on the cell membrane with the transport of substrates and ions through the cell membrane, resulting in antibacterial activity against S. pneumoniae cells.
62 citations
TL;DR: The structure and mechanism of formation of a novel hexagonal mesostructured vanadium oxide−surfactant composite (HMVO), synthesized by acid-catalyzed hydrolysis of ethanolic cetyltrimethylammonium vanadate (CTAV) solution, has been studied by a variety of spectroscopic techniques as mentioned in this paper.
Abstract: The structure and mechanism of formation of a novel hexagonal mesostructured vanadium oxide−surfactant composite (HMVO), synthesized by acid-catalyzed hydrolysis of ethanolic cetyltrimethylammonium vanadate (CTAV) solution, has been studied by a variety of spectroscopic techniques. The poorly crystalline CTAV precursor used in the synthesis has been characterized and is shown to consist of pyrovanadate-like anions in which one oxygen atom is shared between vanadate tetrahedra. The HMVO formed from this precursor appears to feature a distorted octahedral vanadium coordination similar to that found in extended structures such as the two-dimensional vanadium pentoxide gel network. Information on the solution speciation during the synthesis is monitored by 51V NMR spectroscopy. Prior to acid addition, the ethanolic solution of CTAV shows a single narrow resonance at −556.7 ppm, assigned to a tetrahedral diester anion [VO2(OEt)2]-, undergoing fast reorientational averaging of the quadrupole interaction in solu...
57 citations
TL;DR: A kinetic analysis of H-pumping and H+-leakage indicated that the reconstituted epicotyl V-ATPase exhibited twice as much intrinsic uncoupling or slip as the reconStituted fruit V- ATPase.
TL;DR: It is demonstrated that the antilipolytic effect of vanadate differs from that of insulin at least by the five following criteria:Vanadate inhibits lipolysis mediated by high (supraphysiological) concentrations of catecholamines; vansadate antagonizes (Bu)2cAMP-mediated Lipolysis; vanadates antagonizes isobutylmethylxanthine-dependent lipolytic activity; and wortmannin fails to block vanadATE
Abstract: Vanadate, which mimics the biological effects of insulin, also inhibits lipolysis in rat adipocytes. Here we demonstrate that the antilipolytic effect of vanadate differs from that of insulin at least by the five following criteria: 1) vanadate inhibits lipolysis mediated by high (supraphysiological) concentrations of catecholamines; 2) vanadate antagonizes (Bu)2cAMP-mediated lipolysis; 3) vanadate antagonizes isobutylmethylxanthine-dependent lipolysis, 4) vanadate inhibits lipolysis mediated by okadaic acid; and 5) wortmannin, which blocks the antilipolytic effect of insulin, fails to block vanadate-mediated antilipolysis. Vanadate does activate phosphoinositol 3-kinase, and wortmannin blocks this activation. Our working hypothesis assumes that all of the insulin-like effects of vanadate, including antilipolysis, are initiated by the inhibition of protein phosphotyrosine phosphatases (PTPases). Among documented PTPase inhibitors we found that VOSO4 (oxidation state +4), several organic vanadyl compounds ...
TL;DR: Findings give strong confirmation of the concepts that in intact Pgp both nucleotide sites are active in MgATP hydrolysis, and that they interact strongly.
Abstract: ATPase activity of P-glycoprotein (multidrug-resistance protein) was found to be potently inhibited by beryllium fluoride (BeFx) in combination with MgATP, MgADP, or corresponding Mg-8-azido-nucleotides. Inhibition was due to trapping of nucleoside diphosphate at catalytic sites. Full inhibition was achieved on trapping of 1 mol of nucleotide per mol of Pgp. Reactivation was slow (t(1/2) = 32 min at 37 degrees C), and release of trapped nucleotide correlated with recovery of ATPase. Trapping of 8-azido-ADP followed by UV irradiation yielded permanent inactivation and specific labeling of Pgp in plasma membranes. Both N- and C-terminal nucleotide binding sites were labeled. These findings give strong confirmation of the concepts that in intact Pgp both nucleotide sites are active in MgATP hydrolysis, and that they interact strongly. The characteristics of inhibition by BeFx were similar in general to those seen with vanadate. However, PPi gave strong protection against BeFx inhibition, and in this respect, inhibition by BeFx was clearly different from vanadate inhibition.
TL;DR: In this article, vanadate-activated protein tyrosine kinase (MembPTK) was found to be associated with hexose uptake and antilipolytic activity.
Abstract: The insulin-like effects of vanadate are independent of the insulin receptor and insulin receptor substrate 1 (IRS-1) phosphorylation. A cytosolic protein tyrosine kinase (CytPTK), sensitive to inhibition by nanomolar concentrations of staurosporine (concentration at which 50% inhibition occurs [IC 50 ], 1–2 nmol/1), has been implicated in some (i.e., glucose oxidation, lipogenesis) but not all (i.e., hexose uptake, inhibition of lipolysis) of the insulin-like effects of vanadate. We report here the existence of another nonreceptor protein tyrosine kinase in rat adipocytes, located exclusively in the plasma membranes (MembPTK), which we suggest is associated with hexose uptake and the antilipolytic activity of vanadate. MembPTK is a nong-lycoprotein with an estimated molecular weight of 55–60 kDa. In a cell-free experiment, vanadate activates MembPTK seven- to ninefold (median effective dose, 17 ± 2 μmol/l). Vanadate-activated MembPTK is inhibited by staurosporine (IC 50 , 60 ± 5 nmol/l). In intact adipocytes, staurosporine antagonized vanadate-induced hexose uptake (IC 50 , 6.0 ± 0.3 μmol/l) and significantly reversed the antilipolytic effect of vanadate (IC 50 , 5.0 ± 0.4 μmol/l). After vanadate treatment, a phosphorylated P55 protein is immunoprecipitated by antibodies to both phosphotyrosine and phosphatidyli-nositol (PI) 3-kinase. In conclusion, rat adipocytes contain an additional vanadate-activatable nonreceptor membranous protein tyrosine kinase that may participate in the effects of vanadate not carried out by CytPTK. We also suggest that after treatment with vanadate, MembPTK is activated by autophosphorylation and interacts with PI 3-kinase. This may explain how vanadate activates PI 3-kinase without involving receptor activation and IRS-1 phosphorylation.
TL;DR: The manganese uptake inhibition by nifedipine, a calcium channel blocker, for the case of vanadate treated erythrocytes, suggests that, at least partially, manGANese uptake by the cells occurs via the 'calcium channels'.
TL;DR: The results indicate that the increase in apparent affinity for ATP effected by the Ser775 → Ala mutation is secondary to a change in intrinsic cation affinity/selectivity.
TL;DR: It is hypothesized that the mutations conferred resistance because the altered plasma membrane H+-ATPase could more efficiently rid the cell of toxic levels of Ca2+ or protons or other ions accumulated in the cytoplasm following inactivation of the V- ATPase by CCA.
TL;DR: It is indicated that procyclic forms of Trypanosoma brucei possess a phosphatase activity detected in the external cell surface able to hydrolyze about 0.7 nmol ∙ mg−1 p-nitrophenylphosphate, and that intact cells could catalyze the dephosphorylation of [32P]phosphocasein phosphorylated at serine and threonine residues.
Abstract: The results presented in this paper indicate that procyclic forms of Trypanosoma brucei possess a phosphatase activity detected in the external cell surface able to hydrolyze about 0.7 nmol.mg-1.min-1 p-nitrophenylphosphate. A faster rate of hydrolysis was observed when membrane-enriched fractions were used. This activity is weakly sensitive to 1 mM NaF, 10 mM tartrate and 10 mM levamizole but strongly inhibited by 0.1 mM vanadate. Inhibition by both NaF and vanadate have a competitive character. This phosphatase activity decreases by increasing the pH from 6.8 to 8.4, a pH range in which cell viability was maintained during at least 1 hour. In the membrane-enriched fractions this phosphatase activity showed to be an acid phosphatase. In addition, intact cells could catalyze the dephosphorylation of [32P]phosphocasein phosphorylated at serine and threonine residues.
TL;DR: Maltol vanadium derivatives behave in a similar way to vanadate and vanadyl in osteoblast-like UMR 106 cells in culture, and directly inhibited bovine intestinal ALP with a similar potency.
TL;DR: The highly conserved lysine residue Lys758 in the fifth stalk segment of the sarcoplasmic reticulum Ca2+-ATPase was substituted with either isoleucine or arginine by site-directed mutagenesis, and multiple changes of functional characteristics were observed with the Lys758→ Ile mutant.
TL;DR: The data confirm a requirement for intra- and extracellular Ca2+ in neutrophil respiratory burst activation via the kinase/phosphatase cycle, and an agonist effect by NMDA within the Ca2+, leading to generation of the respiratory burst as monitored by luminol-dependent chemiluminescence.
Abstract: Activation of neutrophil oxidases, including NADPH oxidase, is Ca2+ dependent. The aim of this study was to determine the roles of intra- and extracellular Ca2+, leading to generation of the respiratory burst, as monitored by luminol-dependent chemiluminescence (CL). All results were recorded as integrals (millivolt.min) and compared by a two-tail Student's t test. Preincubation of cells with chelators of intra- or extracellular Ca2+ inhibited N-Formyl-Met-Leu-Phe (FMLP)-stimulated burst activity (p < 0.01). In contrast, stimulation by phorbol myristate acetate (PMA), while inhibited by extracellular Ca2+ chelation with EGTA (p < 0.001), was potentiated by intracellular Ca2+ chelation with BAPTA (p < 0.01). This suggests that the protein kinase C (PKC)-mediated burst may be diminished by intracellular Ca(2+)-dependent phosphatase. A selective inhibitor of tyrosine phosphatase, sodium vanadate, potentiated CL generation by both FMLP and PMA, indicating a dominant phosphatase activation with transiently increased Ca2+, masking the kinase-mediated respiratory burst. The selective inhibitors of PKC or tyrosine kinase prevented PMA and vanadate/PMA stimulation (p < 0.005). Furthermore, the putative Ca2+ channel agonists glutamate (10(-5)M) and N-methyl-D-aspartate (NMDA) (10(-5)M) alone failed to influence CL output, but produced marked potentiation following pre-treatment with vanadate. Again this indicates a dominant activation of phosphatase triggered by the glutamate-mediated Ca2+ influx, so masking the kinase-dependent NADPH oxidase activity. A competitive antagonist of NMDA, AP7, significantly decreased vanadate-mediated CL in an EGTA-sensitive manner (p < 0.001). The data confirm a requirement for intra- and extracellular Ca2+ in neutrophil respiratory burst activation via the kinase/phosphatase cycle, and an agonist effect by NMDA within the Ca2+ cascade mechanism.
TL;DR: The location of the ATP-binding site of a P-type ion pump, Ca(2+)-ATPase from rabbit sarcoplasmic reticulum, was examined by cryoelectron microscopy and statistical comparison of the structures with and without CrATP showed clear and significant differences at the groove proposed previously as the ATP.
TL;DR: In this article, the authors used a refined method and experimental protocols which allowed continuity in the estimates of [Ca2+]i, from nanomolar to millimolar concentrations, in the presence and absence of external Ca2+ chelators.
Abstract: 1. Precise knowledge of the cytoplasmic Ca2+ buffering behaviour in intact human red cells is essential for the characterization of their [Ca2+]i-dependent functions. This was investigated by using a refined method and experimental protocols which allowed continuity in the estimates of [Ca2+]i, from nanomolar to millimolar concentrations, in the presence and absence of external Ca2+ chelators. 2. The study was carried out in human red cells whose plasma membrane Ca2+ pump was inhibited either by depleting the cells of ATP or by adding vanadate to the cell suspension. Cytoplasmic Ca2+ buffering was analysed from plots of total cell calcium content vs. ionized cytoplasmic Ca2+ concentration ([CaT]i vs. [Ca2+]i) obtained from measurements of the equilibrium distribution of 45Ca2+ at different external Ca2+ concentrations ([Ca2+]o), in conditions known to clamp cell volume and pH. The equilibrium distribution of 45Ca2+ was induced by the divalent cation ionophore A23187. 3. The results showed the following. (i) The known red cell Ca2+ buffer represented by alpha, with a large capacity and low Ca2+ affinity, was the main cytoplasmic Ca2+ binding agent. (ii) The value of alpha was remarkably constant; the means for each of four donors ranged from 0.33 to 0.35, with a combined value of all independent measurements of 0.34 +/- 0.01 (mean +/- S.E.M., n = 16). This contrasts with the variability previously reported. (iii) There was an additional Ca2+ buffering complex with a low capacity (approximately 80 micromol (340 g Hb)(-1)) and intermediate Ca2+ affinity (apparent dissociation constant, K(D,app) approximately 4-50 microM) whose possible identity is discussed. (iv) The cell content of putative Ca2+ buffers with submicromolar Ca2+ dissociation constants was below the detection limit of the methods used here (less than 2 micromol (340 g Hb)(-1)). 4. Vanadate (1 mM) inhibited the Vmax of the Ca2+ pump in inosine-fed cells by 99.7%. The cytoplasmic Ca2+ buffering behaviour in these cells was similar to that found in ATP-depleted cells.
TL;DR: Data suggest that the oxidation state and coordination geometry of vanadium determine the degree of the cytotoxic-like effect of the vanadium compounds.
Abstract: Vanadium compounds are shown to have a mitogenic effect on fibroblast cells. The effects of vanadate, vanadyl and pervanadate on the proliferation and morphological changes of Swiss 3T3 cells in culture are compared. Vanadium derivatives induced cell proliferation in a biphasic manner, with a toxic-like effect at doses over 50mM, after 24h of incubation. Vanadyl and vanadate were equally potent at 2.5–10mM. At 50mM vanadate inhibited cell proliferation, whereas slight inhibition was observed at 100mM of vanadyl. At 10mM pervanadate was as potent as vanadate and vanadyl in stimulating fibroblast proliferation, but no effect was observed at lower concentrations. A pronounced cytotoxic-like effect was induced by pervanadate at 50mM. All of these effects were accompanied by morphological changes: transformation of fibroblast shape from polygonal to fusiform; retraction with cytoplasm condensation; and loss of lamellar processes. The magnitude of these transformations correlates with the potency of vanadium derivatives to induce a cytotoxic-like effect: pervanadate>vanadate>vanadyl. These data suggest that the oxidation state and coordination geometry of vanadium determine the degree of the cytotoxicity.
TL;DR: A model for the behaviour of vanadium complexes in vivo is generated, providing a basis for the rational design and synthesis of new vanadium-based agents as insulin mimics and becomes complexed to a wide range of intracellular binding sites.
Abstract: The action of vanadate on intact human erythrocytes was studied by 1H spin echo and 51V NMR spectroscopy as a model for the behaviour of vanadium(V) complexes in experimental diabetes. Vanadate is reduced by the intact erythrocyte at the expense of intracellular glutathione which rapidly depletes from the intracellular volume. Using the blocking agent 4,4′-diisothio-cyanatostilbene-2,2′-disulfonic acid (DIDS), which specifically blocks the anion transporter, vanadate reduction could be inhibited and glutathione depletion arrested. Thus, for the reaction with the intact cell to occur, vanadium(V) must cross the cell wall, possibly via the anion transporter. Nitrofurantoin was used to inhibit glutathione reductase in the erythrocyte suspensions. Under these conditions, treatment of the cells with vanadate induced glutathione oxidation prior to depletion. A study of the reaction of vanadate with haemolysate indicates that, without the influence of the membrane, rapid oxidation of glutathione to glutathione disulfide by the vanadyl cation occurs with no glutathione depletion, and that under these conditions vanadate reduction is incomplete. This study generates a model for the behaviour of vanadium complexes in vivo, providing a basis for the rational design and synthesis of new vanadium-based agents as insulin mimics. In essence, vanadium is transported across the membrane as vanadate(V), is reduced in situ by glutathione, and becomes complexed to a wide range of intracellular binding sites. Exchange reactions between glutathione and sulfhydryl groups present on haemoglobin and membrane lead to the depletion of glutathione from the cytosol.
TL;DR: The potential biological activity of vanadium analogs of AMP, ADP, ATP, 2',3''-cAMP, and 3',5'-'cAMP was investigated in aqueous solution using a combination of potentiometry (glass electrode) and 51V NMR spectroscopy.
Abstract: The potential biological activity of vanadium analogs of AMP, ADP, ATP, 2‘,3‘-cAMP, and 3‘,5‘-cAMP stimulated the full speciation study of the vanadate−adenosine(AdH) and vanadate−adenosine−imidazole(ImH) systems in aqueous solution, using a combination of potentiometry (glass electrode) and 51V NMR spectroscopy. The study of the H+−H2VO4-−AdH−ImH system was performed in 0.600 M Na(Cl) medium at 25 oC in the pH range 2−11. In the vanadate−adenosine system V2Ad22- and a new complex, V2Ad2-, with log β = 7.68 ± 0.01 and 11.89 ± 0.08, respectively (pKa = 4.21), explained all experimental observations. Although the V2Ad2--type complex has previously been reported in the vanadate−AMP system, the existence of such a complex in a vanadate−nucleoside system was not previously appreciated. In the vanadate−adenosine−imidazole system a ternary mixed ligand complex, VAdIm-, forms in addition to the V2Ad22- and V2Ad2- species. It exists between pH 5.5 and 11 and has a formation constant log β = 3.04 ± 0.02. This is th...
TL;DR: It is demonstrated that regucalcin, which is expressed in rat kidney cortex, can increase Ca2-ATPase activity and Ca2+ uptake in the basolateral membranes.
Abstract: The effect of regucalcin, a calcium-binding protein, on ATP-dependent Ca2+ transport in the basolateral membranes isolated from rat kidney cortex was investigated. The prepared membranes were in inside-out oriented and membrane vesicles. Ca2+-ATPase activity in the basolateral membranes was progressively elevated by increasing concentrations of regucalcin (10-8 to 10-6 M) in the reaction mixture. This increase was dependent on Ca2+ addition. The activatory effect of regucalcin on the enzyme is inhibited by the presence of digitonin (5 × 10-6%) which can solubilize the membranous lipids. Moreover, the regucalcin effect was clearly abolished by the presence of vanadate (0.1 mM) or N-ethylmaleimide (5.0 mM). However, the effect of calmodulin (6 × 10-7 M) to increase Ca2+-ATPase activity was not significantly inhibited by vanadate or N-ethylmaleimide, indicating that the action mode of regucalcin differs from that of calmodulin. Also, the activatory effect of regucalcin on Ca2+-ATPase was appreciably inhibited by addition of dibutyryl cAMP (10-5 and 10-3 M), while inositol 1,4,5-trisphosphate (10-7 and 10-5 M) had no effect. Dibutyryl cAMP itself did not have an effect on the enzyme activity. Furthermore, the 45Ca2+ uptake by the basolateral membranes was clearly increased by the presence of regucalcin (10-7 and 10-6 M). This increase was completely blocked by the presence of vanadate (0.1 mM), N-ethylmaleimide (5.0 mM) or dibutyryl cAMP (10-4 and 10-3 M) in the reaction mixture. These results clearly demonstrate that regucalcin, which is expressed in rat kidney cortex, can increase Ca2+-ATPase activity and Ca2+ uptake in the basolateral membranes. Regucalcin may play a cell physiologic role as an activator in the ATP-dependent Ca2+ pumps in the basolateral membranes from rat kidney cortex.
TL;DR: It is concluded that at least one more Ca 2+ /Mg 2+ -dependent ATP-hydrolase, in addition to H + -ATPase, is associated with the PBM, and this enzyme is likely responsible for the observed background that masks ATP-Hydrolyzing activity of the P BM.
TL;DR: It is concluded that vanadate acts directly on human bronchial smooth muscle, promoting the release of Ca2+ from an intracellular store and inhibiting the spasmogenic effect ofVanadate.
Abstract: 1. Inhalation of vanadium compounds, particularly vanadate, is a cause of occupational bronchial asthma. We have now studied the action of vanadate on human isolated bronchus. Vanadate (0.1 microM-3 mM) produced concentration-dependent, well-sustained contraction. Its -logEC50 was 3.74 +/- 0.05 (mean +/- s.e.mean) and its maximal effect was equivalent to 97.5 +/- 4.2% of the response to acetylcholine (ACh, 1 mM). 2. Vanadate (200 microM)-induced contraction of human bronchus was epithelium-independent and was not inhibited by indomethacin (2.8 microM), zileuton (10 microM), a mixture of atropine, mepyramine and phentolamine (each at 1 microM), or by mast cell degranulation with compound 48/80. 3. Vanadate (200 microM)-induced contraction was unaltered by tissue exposure to verapamil or nifedipine (each 1 microM) or to a Ca2+-free, EGTA (0.1 mM)-containing physiological salt solution (PSS). However, tissue incubation with ryanodine (10 microM) in Ca2+-free, EGTA (0.1 mM)-containing PSS reduced vanadate-induced contraction. A series of vanadate challenges was made in tissues exposed to Ca2+-free EGTA (0.1 mM)-containing PSS with the object of depleting intracellular Ca2+ stores. In such tissues cyclopiazonic acid (CPA; 10 microM) prevented Ca2+-induced recovery of vanadate-induced contraction. 4. Tissue incubation in K+-rich (80 mM) PSS, K+-free PSS, or PSS containing ouabain (10 microM) did not alter vanadate (200 microM)-induced contraction. Ouabain (10 microM) abolished the K+-induced relaxation of human bronchus bathed in K+-free PSS. This action was not shared by vanadate (200 microM). The tissue content of Na+ was increased and the tissue content of K+ was decreased by ouabain (10 microM). In contrast, vanadate (200 microM) did not alter the tissue content of these ions. Tissue incubation in a Na+-deficient (25 mM) PSS or in PSS containing amiloride (0.1 mM) markedly inhibited the spasmogenic effect of vanadate (200 microM). 5. Vanadate (200 microM)-induced contractions were markedly reduced by tissue treatment with each of the protein kinase C (PKC) inhibitors H-7 (10 microM), staurosporine (1 microM) and calphostin C (1 microM). Genistein (100 microM), an inhibitor of protein tyrosine kinase, also reduced the response to vanadate. 6 Vanadate (0.1-3 mM) and ACh (1 microM- 3 mM) each increased inositol phosphate accumulation in bronchus. Such responses were unaffected by a Ca2+-free medium either alone or in combination with ryanodine (10 microM). 7. In human cultured tracheal smooth muscle cells, histamine (100 microM) and vanadate (200 microM) each produced a transient increase in intracellular Ca2+ concentration ([Ca2+]i). 8. Intracellular microelectrode recording showed that the contractile effect of vanadate (200 microM) in human bronchus was associated with cellular depolarization. 9. It is concluded that vanadate acts directly on human bronchial smooth muscle, promoting the release of Ca2+ from an intracellular store. The Ca2+ release mechanism involves both the production of inositol phosphate second messengers and inhibition of Ca-ATPase. The activation of PKC plays an important role in mediating vanadate-induced contraction at values of [Ca2+]i that are close to basal.
TL;DR: Vanadate and chromate reduction in the presence of biocomponents like saccharides and L-ascorbic acid is demonstrated to generate V(IV) and Cr(III) species, respectively, which may lead to a better understanding of the toxic effects of the corresponding metal ions.