Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Vanadates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed1996

Stimulation of inorganic phosphate transport by insulin-like growth factor I and vanadate in opossum kidney cells is mediated by distinct protein tyrosine phosphorylation processes.

Insulin-like growth factor I (IGF-I) stimulates sodium-dependent inorganic phosphate (Pi) transport across the apical plasma membrane of confluent opossum kidney (OK) cells. Previous studies indicated that vanadate, at doses known to inhibit protein tyrosine phosphatases, mimicked the effect of IGF-I and suggested the involvement of tyrosine phosphorylation processes in Pi transport regulation. In this study, protein tyrosine phosphorylation and activation of several cellular signaling pathways were investigated in confluent OK cells in response to IGF-I and vanadate. We report that IGF-I and vanadate induced tyrosine phosphorylation of distinct proteins. Tyrosine phosphorylation of p95 (IGF-I receptor beta-subunit) was rapidly and dose dependently increased in response to IGF-I. Associated with phosphorylation of the receptor, the increase in tyrosine phosphorylation of a protein of 50 kDa was observed. Vanadate did not mimic the effect of IGF-I, but increased phosphorylation of seven major proteins of 170, 140, 100, 83, 70-82, 60, and 35 kDa. Among the different tyrosine kinase inhibitors tested, only staurosporine affected Pi transport up-regulation by IGF-I and vanadate, attenuating the effect of IGF-I and completely blocking the response to vanadate. Staurosporine decreased tyrosine phosphorylation of several constitutively phosphorylated proteins and interfered with the increase in tyrosine phosphorylation induced by vanadate. Phosphorylation of p95 in response to IGF-I was not affected. Staurosporine also markedly decreased constitutive association of the adapter protein Nck with tyrosine-phosphorylated proteins and attenuated increases in phosphotyrosine-associated Nck induced by IGF-I and vanadate. In contrast, signaling to other downstream effectors common to IGF-I and vanadate, such as mitogen-activated protein kinase and phosphatidylinositol-3-kinase, was not affected by staurosporine. In conclusion, our results suggest that although IGF-I and vanadate induce distinct protein tyrosine phosphorylation in OK cells, they activate an overlapping set of signaling molecules, among which Nck appears as an interesting candidate to link activation of tyrosine kinases to the stimulation of Pi transport.

Adaptor Proteins, Signal Transducing↗
PubMed1994

Vanadate action on renal phosphate transport.

Insulin stimulates reabsorption of phosphate (Pi) in the renal proximal tubule. Previous studies have shown that vanadate can mimic the action of insulin on various tissues. In the present study, we tested the action of vanadate on renal Pi transport both in control rats and in rats made diabetic by injection of streptozotocin. Vanadate was administered orally for 4 days by inclusion in drinking water (0.7 mg/ml). By the 4th day, vanadate treatment of control rats did not change acid-base status, plasma glucose or the filtered load of Pi, but the urinary excretion of Pi was reduced to 2.5 +/- 0.9 compared with 17.6 +/- 3.5 mumol/mg creatine (P < 0.02) in untreated control rats. However, Na+/Pi cotransport by isolated brush border membrane vesicles was not different between the two groups. Findings in parathyroidectomized rats were similar. By the 4th day of vanadate treatment of diabetic rats, there was reversal of polyuria, polydipsia and hyperglycemia with no change in acid-base status. The filtered load of Pi was decreased by vanadate, and urinary Pi excretion also tended to decrease but not significantly. The values for Pi excretion were 21.4 +/- 7.6 in vanadate treated diabetics and 36.1 +/- 4.5 mumol/mg creatinine in untreated diabetics. In contrast to vanadate, daily injections of insulin did not change the filtered load of Pi but reduced urinary Pi excretion in diabetic rats to 15.6 +/- 2.2 mumol/mg creatinine (P < 0.02). These findings suggest that vanadate stimulated tubular Pi reabsorption in control rats but not in diabetic rats. Vanadate treatment of diabetic rats may tend to decrease tubular Pi reabsorption in contrast to the action of insulin.

Acid-Base Equilibrium↗
PubMed2000

Substrates of semicarbazide-sensitive amine oxidase co-operate with vanadate to stimulate tyrosine phosphorylation of insulin-receptor-substrate proteins, phosphoinositide 3-kinase activity and GLUT4 translocation in adipose cells.

It has been shown that the combination of benzylamine or tyramine and low concentrations of vanadate markedly stimulates glucose transport in rat adipocytes by a mechanism that requires semicarbazide-sensitive amine oxidase (SSAO) activity and H(2)O(2) formation. Here we have further analysed the insulin-like effects of the combination of SSAO substrates and vanadate and we have studied the signal-transduction pathway activated in rat adipocytes. We found that several SSAO substrates (benzylamine, tyramine, methylamine, n-decylamine, histamine, tryptamine or beta-phenylethylamine), in combination with low concentrations of vanadate, stimulate glucose transport in isolated rat adipocytes. Furthermore, SSAO substrates together with vanadate stimulated the recruitment of GLUT4 to the cell surface in isolated rat adipocytes. Benzylamine plus vanadate also stimulated glucose transport and GLUT4 translocation in 3T3-L1 adipocytes. Benzylamine or tyramine in combination with vanadate potently stimulated the tyrosine phosphorylation of both insulin receptor substrate (IRS)-1 and IRS-3. In contrast, benzylamine and vanadate caused only a weak stimulation of insulin receptor kinase. Benzylamine or tyramine in combination with vanadate also stimulated phosphoinositide 3-kinase activity; wortmannin abolished the stimulatory effect of benzylamine and vanadate on glucose transport in adipose cells. Furthermore, the administration of benzylamine and vanadate in vivo caused a rapid lowering of plasma glucose levels, which took place in the absence of alterations in plasma insulin. On the basis of these results we propose that SSAO activity regulates glucose transport in adipocytes. SSAO oxidative activity stimulates glucose transport via the translocation of GLUT4 carriers to the cell surface, resulting from a potent tyrosine phosphorylation of IRS-1 and IRS-3 and phosphoinositide 3-kinase activation. Our results also indicate that substrates of SSAO might regulate glucose disposal in vivo.

3T3 Cells↗
PubMed2002

The effect of vanadate on Pichia pastoris growth, protein kinase A activity and ribosomal protein phosphorylation.

It was found that wild type yeast Pichia pastoris can tolerate vanadate concentration as high as 25 mM in the growth medium. Moreover, four vanadate-resistant P. pastoris strains designated JC100/1, JC100/3, JC100/9 and JC100/15 exhibiting tolerance up to 150 mM vanadate were selected. Growth of P. pastoris was correlated with vanadate to vanadyl reduction and its accumulation in the growth medium. In two selected strains, JC100/9 and JC100/15, protein kinase A activity was much higher in comparison to the wild type strain even without vanadate addition to the growth medium. Moreover, in the presence of vanadate, protein kinase A activity was significantly increased in the wild type and the vanadate-resistant JC100/1 and JC100/3 strains. It was also found that phosphorylation of a 40 kDa protein associated with ribosomes occured in all vanadate-resistant strains from the logarithmic, while in the wild type strain from the stationary growth phase. From the presented results it can be concluded that a protein kinase A signalling pathway(s) might be involved in the mechanism of P. pastoris vanadate resistance. The results also indicate a possible role of the 40 kDa protein in protection of P. pastoris against vanadate toxicity.

Cell Division↗
PubMed1991

Vanadate stimulation of insulin release in normal mouse islets.

The effects of vanadate (Na3VO4) on pancreatic B-cell function were studied in normal mouse islets. Vanadate did not affect basal insulin release but potentiated the effect of 7-30 mM glucose at concentrations of 0.1-1 mM. This effect was progressive and slowly reversible. It was abolished by omission of extracellular Ca2+ but unaffected by blockers of adrenergic or muscarinic receptors. Comparison of the changes in membrane potential, 86Rb efflux and 45Ca efflux that vanadate and ouabain produced in B-cells made it possible to exclude the hypothesis that vanadate increases insulin release by blocking the sodium pump. Vanadate was also without effect on cAMP levels. On the other hand, it markedly changed the characteristics of the Ca(2+)-dependent electrical activity and of the oscillations of cytoplasmic Ca2+ recorded in B-cells stimulated by 15 mM glucose. In the steady state, Ca2+ influx was increased by vanadate, and this resulted in a rise in cytoplasmic Ca2+. The exact mechanisms underlying these changes could not be established but a blockade of K channels was excluded. In the presence of LiCl, vanadate markedly increased inositol phosphate levels in islet cells. This effect was attenuated but not suppressed by omission of Ca2+. A small increase in inositol bisphosphate was still produced by vanadate in the absence of LiCl. These results suggest that vanadate both stimulates phosphoinositide breakdown and inhibits inositol phosphate degradation. In conclusion, vanadate does not induce insulin release, but markedly potentiates the stimulation by glucose. This property is not due to an inhibition of the sodium pump or to a rise in cAMP concentration. It results from a complex interplay between changes in B-cell membrane potential, phosphoinositide metabolism and Ca2+ handling.

Animals↗
PubMed1986

Modulation by vanadate of the adrenergic characteristics of the iris, ileum, and vas deferens.

The influence of vanadate upon the adrenergic response of the rabbit iris (dilation) was examined in vivo, while the effects of vanadate upon adrenergic responses of the rabbit ileum and guinea pig vas deferens were investigated in vitro. Intravenously administered vanadate (2 mg/Kg) sensitized the iris to topically administered epinephrine; a small quantity of epinephrine, that elicited no change of pupil size following topical administration to the eye in the normal rabbit, produced a marked pupillary dilation in animals treated systemically with vanadate. The response of the isolated ileum to vanadate (1-10 micrograms) was identical to that elicited by norepinephrine or epinephrine. Brief exposure of the ileum to vanadate, norepinephrine, or epinephrine resulted in a transient cessation of rhythmic activity and reduction of mean tension. When the ileum was superfused continuously with solutions containing vanadate (10 micrograms/ml; 5.4 X 10(-5) M), the rhythmic activity and mean tension returned to control values within several minutes, suggesting tachyphylaxis. Exposure of the guinea pig vas deferens to vanadate did not elicit a contractile response. However, when the vas deferens was superfused continuously (greater than 60 min) with vanadate (5.4 X 10(-5) M), both the amplitude and duration of the contraction elicited by epinephrine were increased. Consistent with the above findings is the hypothesis that vanadate might inhibit the mechanisms responsible for the removal of epinephrine or norepinephrine from the site of action within a tissue.

Animals↗
PubMed1985

The influence of reserpine and propranolol upon the IOP response to vanadate in the rabbit.

The authors examined the influence of intravenously administered sodium ortho-vanadate upon the intraocular pressure (IOP) of the albino rabbit. Vanadate was administered by intravenous injection and the IOP was measured by applanation tonometry. Vanadate (2 mg/kg) caused a marked reduction of IOP which lasted for several hours. Pretreatment with systemic reserpine 24 hr prior to vanadate administration markedly diminished ocular hypotensive response to vanadate. Similarly, systemic treatment with propranolol prevented the IOP-lowering effect of vanadate. In addition, propranolol administered during the course of the vanadate-induced hypotensive response caused the IOP to return to a level close to the control value. The IOP-lowering effect of vanadate appeared to be unrelated to cardiovascular changes; vanadate was observed to have no significant influence upon the blood pressure of anesthetized animals even though the IOP was markedly reduced. On the basis of these experiments, the authors suggest that adrenergic mechanisms contribute to the IOP-lowering effect of vanadate.

Animals↗
PubMed1983

Presteady state kinetic analysis of vanadate-induced inhibition of the dynein ATPase.

The effects of vanadate on the kinetics of ATP binding and hydrolysis by Tetrahymena 30 S dynein were examined by presteady state kinetic analysis. Up to a concentration of 400 microM, vanadate did not inhibit the rate or amplitude of the ATP binding-induced dissociation of the microtubule-dynein complex measured by stopped flow light-scattering methods. Chemical quench flow experiments showed that vanadate (80 microM) did not alter the rate or amplitude of the presteady state ATP binding or ATP hydrolysis transients, but the steady state hydrolysis of ATP was blocked immediately after a single turnover of ATP. Preincubation of the enzyme with ADP and vanadate inhibited both presteady state and steady state hydrolysis. These data suggest that vanadate acts as a phosphate analog to form an enzyme-ADP-vanadate complex, analogous to the transition state during catalysis, by the following pathway: (formula; see text) where V represents vanadate and D represents a dynein active site. ADP and vanadate, added together, induced dissociation of the microtubule-dynein complex at a maximum rate of 0.6 S-1. These observations imply that a microtubule-dynein-ADP-vanadate complex was formed which subsequently dissociated as shown below: (formula; see text) where M denotes a microtubule. The ADP plus vanadate-induced dissociation may represent the reverse of the normal forward pathway involving the binding of a dynein-ADP-phosphate complex to a microtubule.

Adenosine Triphosphatases↗
PubMed1984

Vanadate inhibits the ATP-dependent degradation of proteins in reticulocytes without affecting ubiquitin conjugation.

Reticulocytes contain a nonlysosomal, ATP-dependent system for degrading abnormal proteins and normal proteins during cell maturation. Vanadate, which inhibits several ATPases including the ATP-dependent proteases in Escherichia coli and liver mitochondria, also markedly reduced the ATP-dependent degradation of proteins in reticulocyte extracts. At low concentrations (K1 = 50 microM), vanadate inhibited the ATP-dependent hydrolysis of [3H]methylcasein and denatured 125I-labeled bovine serum albumin, but it did not reduce the low amount of proteolysis seen in the absence of ATP. This inhibition by vanadate was rapid in onset, reversed by dialysis, and was not mimicked by molybdate. Vanadate inhibits proteolysis at an ATP-stimulated step which is independent of the ATP requirement for ubiquitin conjugation to protein substrates. When the amino groups on casein and bovine serum albumin were covalently modified so as to prevent their conjugation to ubiquitin, the derivatized proteins were still degraded by an ATP-stimulated process that was inhibited by vanadate. In addition, vanadate did not reduce the ATP-dependent conjugation of 125I-ubiquitin to endogenous reticulocyte proteins, although it markedly inhibited their degradation. In intact reticulocytes vanadate also inhibited the degradation of endogenous proteins and of abnormal proteins containing amino acid analogs. This effect was rapid and reversible; however, vanadate also reduced protein synthesis and eventually lowered ATP levels in the intact cells. Vanadate (10 mM) has also been reported to decrease intralysosomal proteolysis in hepatocytes. However, in liver extracts this effect on lysosomal proteases required high concentrations of vanadate (K1 = 500 microM) and was also observed with molybdate, unlike the inhibition of ATP-dependent proteolysis in reticulocytes.

Adenosine Triphosphate↗
PubMed1997

Ca(2+)-activated K+ channel and the activation of Ca2+ influx in vanadate-treated red blood cells.

The mechanism by which K+ inhibits vanadate-induced 45Ca2+ influx by human red blood cells (RBC) was studied using several independent approaches. The following results were found: 1. The inhibitory effect of K+ was absent when RBC were loaded with a Ca(2+)-chelator. This treatment at the same time inhibited the vanadate-induced K+ efflux, and the membrane hyperpolarization induced by Ca2+ in vanadate-treated cells. 2. The potency of K+, Rb+, and Cs+ to inhibit vanadate-induced Ca2+ influx corresponded to their ability to depolarize the RBC membrane via the Ca(2+)-activated K+ channel (K(Ca)). 3. Inhibition of the vanadate-induced 45Ca2+ influx by a protonophore proceeded in parallel with the inhibition of the vanadate-plus-Ca(2+)-induced membrane hyperpolarization. 4. Valinomycin in part released the inhibition of the vanadate-induced Ca2+ influx by known K(Ca) inhibitors (quinine, oligomycin, 4-aminopyridine) but not by inhibitors of the Ca2+ channel (Cu2+, HS-reagents, organic Ca2+ channel blockers). 5. K+ did not inhibit the vanadate-induced Ca2+ influx in dog RBC which have K(Ca) but no transmembrane K+ gradient. The inhibition of the vanadate-induced Ca2+ influx by external K+ appears to be due to the elimination of the electrical component of the Ca(2+)-motive force imposed by opening of the K(Ca). This implies that the Ca2+ carrier mediating the influx of Ca2+ in the presence of vanadate is of uniport type, and that the activity of K(Ca) may serve as a supporting element for Ca2+ influx.

Aminoquinolines↗
PubMed1989

Effects of vanadate on tyrosine phosphorylation and the pattern of glycosaminoglycan synthesis in rabbit chondrocytes in culture.

The present study examined the effects of high doses of vanadate on glycosaminoglycan (GAG) synthesis and tyrosine phosphorylation in rabbit chondrocytes in confluent cultures. Although 6 microM vanadate increased the incorporation of [3H]glucosamine into chondroitin sulfate proteoglycans twofold, 40-60 microM vanadate suppressed this incorporation fourfold. Although 6 microM vanadate had little effect on [3H]glucosamine incorporation into hyaluronate, 40-60 microM vanadate increased this incorporation threefold. Chemical analyses confirmed that the increase in [3H]glucosamine incorporation into hyaluronate and the decrease in the incorporation into chondroitin sulfate proteoglycan correlated with increased hyaluronate content and decreased chondroitin sulfate content in the cell layers of vanadate-transformed cells. Chondrocytes exposed to 40-60 microM vanadate became typically transformed spindlelike cells. Furthermore, vanadate, at 6 and 60 microM, increased the overall level of phosphotyrosine by 8- and 31-fold, respectively, and 60 microM vanadate enhanced phosphorylation of many phosphotyrosine-containing proteins. These observations suggest that vanadate induces transformation-associated changes in the pattern of GAG synthesis when it induces excess phosphorylation on tyrosine in chondrocyte proteins.

Animals↗
PubMed1999

Vanadate and the absence of myofibroblasts in wound contraction.

HYPOTHESIS: Fibroblasts, not myofibroblasts, are responsible for wound contraction. Only myofibroblasts express a smooth muscle actin for which vanadate blocks its expression. Wound contraction in vanadate-treated rats will proceed normally in the absence of myofibroblasts. DESIGN: Laboratory study using rats. METHODS: Wound healing in rats receiving vanadate parenterally, an inhibitor of tyrosine phosphate phosphatases, was investigated. For 21 days, treated rats received drinking water containing vanadate, 0.2 mg/mL, in isotonic sodium chloride solution, and the control rats received isotonic sodium chloride solution alone. On day 7, 4 square, full-excision wounds were made dorsally and measured, then 2 polyvinyl alcohol sponges were placed ventrally in subcutaneous pockets. RESULTS: After 2 weeks, the wound area in the rats receiving vanadate measured 7.1 +/- 1.8 U (mean+/-SD), and the wound area in the control rats measured 7.2 +/- 2.2 U. The control rats' granulation tissue (GT) had myofibroblasts, or alpha-smooth muscle (alpha-SM) actin-positive fibroblasts, whereas the vanadate-treated group's fibroblasts were devoid of alpha-SM actin. By Western blot analysis, GT homogenates in the vanadate-treated group contained less alpha-SM actin. By electron microscopy, control rats' GT showed classic myofibroblast populations, and the collagen fiber bundles were randomly organized. In contrast, the wounds in the vanadate-treated group showed unencumbered fibroblast populations and neatly ordered, parallel collagen fiber bundles. By polarized light microscopy, the GT of the vanadate-treated group displayed orderly collagen fiber bundles. CONCLUSIONS: The differentiation of fibroblasts into myofibroblasts requires the dephosphorylation of selected tyrosine phosphate residues. In the absence of myofibroblasts, the rate of rat wound contraction is normal, and collagen fiber bundles have a more orderly arrangement. Myofibroblasts are not required for wound contraction.

Animals↗
PubMed1993

Vanadate-induced contraction of smooth muscle and enhanced protein tyrosine phosphorylation.

This study was guided by the hypothesis that protein tyrosine phosphorylation may participate in signal transduction that is associated with contraction of smooth muscle. Accordingly, because sodium vanadate stimulates contraction of smooth muscle and inhibits protein tyrosine phosphatases, we sought to determine if vanadate-induced contraction was linked to enhanced protein tyrosine phosphorylation. Pronounced and time-dependent increases (5- to 20-fold) occurred in tyrosine phosphorylation during vanadate-induced contraction of guinea pig taenia coli. Three substrates of 86, 116, and 205 kDa were tyrosine phosphorylated as detected by immunoblotting with phosphotyrosine monoclonal antibody. Vanadate-induced contraction and enhanced protein tyrosine phosphorylation were both reduced in the presence of 2.5-5 micrograms/ml genistein, a potent tyrosine kinase inhibitor. In the continued presence of vanadate, chelation of extracellular Ca2+ with 5 mM ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) caused relaxation. However, pronounced phosphorylation of the substrates persisted even though isometric force decreased to control level. In this setting, replacement of the muscle bathing medium with fresh vanadate and EGTA-free medium caused a prompt spontaneous contraction which was immediately followed by relaxation and dephosphorylation of the substrates. Similarly, blockade of Ca(2+)-entry sites with 10 mM LaCl3 also relaxed smooth muscle strips that had been contracted with 1.5 mM vanadate. However, unlike EGTA-induced relaxation, replacement of the medium with fresh vanadate and LaCl3-free medium did not cause a spontaneous contraction. Taken together, these results show that vanadate-induced contraction of smooth muscle is probably coupled to enhanced protein tyrosine phosphorylation. The results also suggest that tyrosine phosphorylation may participate in Ca(2+)-dependent signalling mechanisms which regulate contraction of smooth muscle.

Animals↗
PubMed1996

Inhibition of a Src homology 2 domain containing protein tyrosine phosphatase by vanadate in the primary culture of hepatocytes.

Inhibition of protein tyrosine phosphatase (PTP) activities by vanadate was examined in cultured rat hepatocytes. The incubation of hepatocytes with sodium orthovanadate inhibited PTP activities, measured with labeled polyglutamate tyrosine (4:1) and insulin receptor peptide (1142-1153), in a dose- and time-dependent manner. The PTP activities in cytosolic and particulate fractions were inhibited with the IC50 values of 30-50 and 2-20 microM, respectively. Vanadate-mediated inhibition of protein phosphatase, type 1 (a serine phosphatase) was less pronounced, requiring 50- to 150-fold higher concentrations. Molybdate and tungstate, the other potent inhibitors of PTPs, exerted approximately 70% less inhibition of enzyme activities compared to vanadate in intact liver cells. The cytosolic and particulate PTPs inhibited by vanadate were further resolved by fast protein liquid chromatography on Mono Q and Superose-12 columns. Vanadate exerted stable and differential inhibition of several PTPs. One of them was identified as SHPTP2 (Syp, SHP-2) in cytosolic as well as particulate fractions. Immunoprecipitation of this PTP with Syp-antibody coupled to protein A-agarose confirmed the vanadate-induced decrease in SHPTP2 activity. Vanadate did not alter the expression of SHPTP2 and its distribution between cytosolic and particulate fractions as indicated by the immunoblots. The decrease in the activities of PTPs in vanadate-treated hepatocytes in general was found to be reversed by the reducing agent dithioerythreitol. This study shows that vanadate inhibits many PTPs in intact liver cells, one of them being SHPTP2/SHP-2. The inhibition is stable after chromatography on ion-exchange and gel filtration chromatography. The enzyme inhibition seems to involve the oxidation of the thiol group of PTPs.

Animals↗
PubMed1999

A two-component affinity chromatography purification of Helix pomatia arylsulfatase by tyrosine vanadate.

The inhibition of Helix pomatia arylsulfatase by the synergistic combination of N-acetyl-l-tyrosine ethyl ester and vanadate has been extended to affinity chromatography for purification. In the presence of vanadate, l-tyrosine ethyl ester (TEE), immobilized on CH-Sepharose 4B retained arylsulfatase from the digestive juice or lyophilized powder of H. pomatia. No enzyme was retained without vanadate or with arsenate or phosphate. Arylsulfatase was eluted from the column matrix by removing the vanadate to less than 50 microM with buffer containing EDTA to chelate the vanadate. Escherichia coli alkaline phosphatase and potato acid phosphatase, two enzymes which are inhibited by vanadate but not by the vanadate-TEE complex, were not retained by the immobilized TEE under any conditions used. The sulfatase activity was completely separated from contaminating glucuronidase activity present in the crude enzyme extracts. The Ki for the immobilized vanadate-TEE system was found to be 5.0 x 10(-7) M with a capacity of 25 mg/ml swollen gel. A purification of greater than 40-fold from the lyophilized powder of H. pomatia (Sigma Type H-5) was achieved using this technique. The Ki/Keq of other phenols with vanadate were determined in a 96-well plate format as an example of a rapid screening technique that could be extended to other phosphoryl and sulfuryl-transfer enzyme classes.

Animals↗
PubMed1980

Possible mechanisms for inotropic actions of vanadate in isolated guinea pig and rat heart preparations.

The mechanism of inotropic actions of vanadate studied in isolated, electrically stimulated atrial and ventricular muscle preparations of rat or guinea-pig heart. Vanadate produced a negative inotropic effect in guinea-pig left atrial preparations associated with a marked shortening of the action potential plateau. In guinea-pig papillary muscle, or rat atrial or ventricular muscle preparations, vanadate produced a positive inotropic effect, which was not affected by either propranolol, phentolamine or metiamide. The positive inotropic effect was observed when action potential duration was either increased or decreased. Inotropic concentrations of vanadate failed to significantly alter the ouabain-sensitive 86Rb+-uptake, an estimate of sodium pump activity, or tissue concentration of cyclic AMP in electrically stimulated preparations. In partially depolarized rat atrial preparations in which fast sodium channels were inactivated in the presence of a high concentration of K+ (22 mmol/l), vanadate restored electrical activity (calcium-dependent action potentials) and the contraction, similar to isoproterenol. This action of vanadate was abolished by Mn2+, a slow channel inhibitor, but not by tetrodotoxin. The characteristic of vanadate- and isoproterenol-restored preparations, however, were substantially different. Moreover, vanadate failed to restore the contraction or action potential in partially depolarized guinea pig atrial preparations unlike isoproterenol. These results indicate that vanadate may either enhance or inhibit slow channels in cardiac muscle.

Action Potentials↗
PubMedDate not supplied

Contractile effects of vanadate on aorta rings from virgin and pregnant rats.

The present study was undertaken to characterize the contractile effects of vanadate on thoracic aorta rings from virgin and term-pregnant rats. Vanadate caused concentration-dependent contraction in rat aortic rings with an EC50 (concentration producing 50% maximum response) of 0.10 mM. Contractions in response to vanadate were equivalent to the ones measured with 1 microM phenylephrine. The effects of vanadate were not affected by indomethacin (up to 10 microM), an inhibitor of prostanoid cyclooxygenase, but were blocked in a concentration-dependent manner by staurosporine (0.1-1.0 microM), an inhibitor of protein kinase C. Vanadate exhibited a significant decrease of contractile responses in aorta of pregnant as compared to virgin rats. When aortic rings were bathed in presence of different concentrations of vanadate, the concentration-response curve to phenylephrine was shifted to the left, but maximum response was not affected. The potentiation of the contractions to phenylephrine by vanadate was significantly more prominent in aorta of virgin than of pregnant rats. These results suggest that the contractile effect of vanadate on rat aorta is independent of endogenous prostanoids and may be mediated by protein kinase C-dependent pathway. These results also show that the contractile response to vanadate on the rat aorta is impaired during pregnancy.

Animals↗
PubMedDate not supplied

Significance of NADH-vanadate-oxidoreductase of cardiac and erythrocyte cell membranes.

Vanadate(V), which has positive inotropic, natriuretic and vasoconstrictive effects, is taken up by cardiac cells and erythrocytes in large quantities. Most of the intracellular vanadium is shown to exist as protein-bound vanadyl(IV), however Vanadate (VO3) is a powerful inhibitor of the (Na+ rK+)-ATPase and the Ca++-ATPase, whereas it stimulates adenylate cyclase of cardiac tissue. Vanadyl (VO2+) has no or much less effects on these enzymes. Plasma membranes of cardiac tissue (cat, calf, human) as well as erythrocytes contain an enzyme that converts vanadate(V) to vanadyl(IV) in the presence of NADH but not NADPH. The optimal conditions for this NADH-vanadate-oxidoreductase are: pH 6.8, 1 mM, NADH, 1.5 mM Va3VO4. Mg++ inhibits the enzyme half-maximally at 3 mM, Ca++ stimulates at low and inhibits at high concentrations (half-maximally at 0.8 mM). The enzyme is supposed to be located at the inner side of the cell membrane. Vanadate has been proposed as an ideal regulator of active cation transport across the cell membrane. The finding of a HADH-vanadate-oxidoreductase converting vanadate into the rather inactive vanadyl further supports this hypotheses. The amount of vanadate at active sites of the target enzymes might be responsible for the known vanadate effects.

Animals↗