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1987 Fluoride Abstracts. Part 1.

Abstracts for the following years:
Part 1 - mainly biochemistry and physiology (brain, hormonal, G-proteins, etc.)
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http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2884018&dopt=Abstract

Brain Res 1987 Apr 28;410(1):116-20

Increase in the stimulation-induced overflow of glutamate by fluoroacetate, a selective inhibitor of the glial tricarboxylic cycle.

Szerb JC, Issekutz B.

Fluoroacetate is known to be taken up selectively by glia, where after forming fluorocitrate, it inhibits the tricarboxylic acid cycle. Since uptake into glia has a major role in the inactivation of synaptically released glutamate, the effect of fluoroacetate on the overflow of glutamate evoked by electrical field stimulation in slices of rat hippocampus was investigated. In agreement with previous reports, 1 mM fluoroacetate reduced the release and content of glutamine, but increased only slightly the overflow of glutamate induced by stimulation. If, however, 0.5 mM glutamine was added to the superfusion fluid, fluoroacetate nearly tripled the overflow of glutamate evoked by electrical field stimulation. The large glutamate overflow due to field stimulation in the presence of fluoroacetate was fully Ca2+ -dependent. Results confirm the major role of glia in the inactivation of glutamate. The absence of such an uptake may contribute to the in vivo convulsive effect of fluoroacetate.

PMID: 2884018 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2822001&dopt=Abstract

Biochem J 1987 May 15;244(1):35-40

Guanine nucleotide and NaF stimulation of phospholipase C activity in rat cerebral-cortical membranes. Studies on substrate specificity.

Litosch I.

Department of Pharmacology, University of Miami School of Medicine, FL 33101.

Guanyl-5'-yl imidodiphosphate (p[NH]ppG) stimulated a rapid phospholipase C-mediated breakdown of exogenously added phosphatidylinositol 4,5-bisphosphate (PIP2) in rat cerebral-cortical membranes, with half-maximal activation at approx. 33 microM. NaF stimulated phospholipase C activity, with half-maximal activation at 0.5 mM. Stimulation of phospholipase C activity by NaF exhibited pH optima at approx. 5.5 and 7.0, with the stimulatory activity at pH 7.0 greater than that at pH 5.5. With p[NH]ppG, only stimulation at pH 7.0 was observed. Neither p[NH]ppG nor NaF stimulated hydrolysis of added phosphatidylinositol (PI) or phosphatidylinositol 4-phosphate (PIP). Mg2+ (0.5 mM) potentiated p[NH]ppG-stimulated breakdown of PIP2. Ca2+ increased basal and p[NH]ppG-stimulated breakdown of PIP2. PI breakdown was stimulated only by high Ca2+ concentrations and was unaffected by p[NH]ppG at any Ca2+ concentration examined. These results indicate that, in cerebral-cortical membranes, activation of phospholipase C by guanine nucleotides or fluoride directly increases a phospholipase C activity which specifically hydrolyses PIP2.

PMID: 2822001 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3328040&dopt=Abstract

Mutagenesis 1987 Nov;2(6):497-9

Sodium fluoride and chromosome damage (in vitro human lymphocyte and in vivo micronucleus assays).

Albanese R.


ICI Pharmaceuticals Division, Macclesfield, Cheshire, UK.

The clastogenic potential of sodium fluoride was determined both in vitro (using cultured human lymphocytes) and in vivo (using the rat bone-marrow micronucleus test). The incidence of chromosome aberrations in human lymphocyte cultures exposed to 20 or 40 micrograms/ml sodium fluoride (3 and 9% respectively) was significantly increased compared with control cultures (0.5%). However, the incidence of micronucleated polychromatic erythrocytes in male AP rats dosed 1000 mg/kg NaF (the maximum tolerated dose over 24 h) or 500 mg/kg NaF was similar to that in the animals dosed distilled water (vehicle control). Thus, sodium fluoride is clastogenic in vitro but not in vivo.

PMID: 3328040 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2826014&dopt=Abstract

Cell 1987 Dec 24;51(6):1053-62

Involvement of GTP-binding "G" proteins in transport through the Golgi stack.

Melancon P, Glick BS, Malhotra V, Weidman PJ, Serafini T, Gleason ML, Orci L, Rothman JE.

Department of Biochemistry, Stanford University, California 94305.

GTP gamma S irreversibly inhibits protein transport between successive compartments of the Golgi stack in a cell-free system. Fluoride, potentiated by the addition of aluminum ion, also causes a strong inhibition. These are hallmarks of the involvement of a guanine nucleotide-binding or regulatory "G" protein. Inhibition by GTP gamma S requires a cytosolic inhibitory factor that binds to Golgi membranes during inhibition. Preincubation experiments reveal that GTP gamma S blocks the function of acceptor Golgi but not donor Golgi membranes. More specifically, a processing step in between vesicle attachment and the actual fusion event seems to be affected. Electron microscopy demonstrates a corresponding 5-fold accumulation of non-clathrin-coated buds and vesicles associated with the Golgi cisternae during inhibition by GTP gamma S.

PMID: 2826014 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3025027&dopt=Abstract

FEBS Lett 1987 Jan 5;210(2):204-10

Carbachol and sodium fluoride, but not TSH, stimulate the generation of inositol phosphates in the dog thyroid.

Graff I, Mockel J, Laurent E, Erneux C, Dumont JE.

In dog thyroid slices prelabeled with myo-[2-3H]inositol, carbachol (10(-7)-10(-4) M) and NaF (10-20 mM) stimulated IP1, IP2 and IP3 generation. These effects did not require the presence of extracellular calcium. Atropine and PDBu inhibited the action of the cholinergic agonist. No effect of TSH (1-100 mU/ml) could be detected on PIP2 hydrolysis and IP production. These results suggest that IP3 could play a role in the metabolic actions of carbachol in the thyroid; a G-protein coupling the hormone-receptor binding to phospholipase C activation exists in the thyroid membrane; the well known TSH-induced increased PI turnover does not result in IP3 accumulation.

PMID: 3025027 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3653065&dopt=Abstract

Environ Res 1987 Oct;44(1):117-25

Effect of sodium fluoride on antibody formation in rabbits.

Jain SK, Susheela AK.

Department of Anatomy, All India Institute of Medical Sciences, New Delhi.

In the present study, the role of sodium fluoride on antibody formation in rabbits is assessed. Sixteen female albino rabbits were divided into four groups and were treated as follows:
Group I: Animals immunized with transferrin and used as controls for group II;
Group II: Animals immunized with transferrin and administered orally NaF (10 mg/kg body weight) daily for 9 months;
Group III: Animals immunized with transferrin and served as controls for group IV; and
Group IV: Animals administered with NaF at a dose of 10 mg/kg body weight daily for 9 months and then immunized with transferrin and fluoride treatment continued for another 9 months.
Rabbits were bled just prior to immunization and subsequent bleeding was at weekly intervals. Circulating anti-transferrin titers were estimated. DNA and protein synthesis was determined by incorporating [3H]thymidine and [14C]leucine, respectively. The present report demonstrates that sodium fluoride inhibits antibody formation in rabbits. There is a threshold level of fluoride (0.78 ppm) in circulation which is responsible for the inhibitory effect on antibody formation. Inhibition of DNA and protein synthesis by NaF is also demonstrated. It is concluded that fluoride inhibits the antibody formation by decreasing the proliferation of lymphocytes and by inhibiting the protein synthetic ability of immunocytes.

PMID: 3653065 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3663865&dopt=Abstract

Biopolymers 1987 Aug;26(8):1347-55

Enthalpy and entropy changes for the intercalation of small molecules to DNA. II. Ethidium and propidium fluoride.

Hopkins HP Jr, Wilson WD.

PMID: 3663865 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2443321&dopt=Abstract

Zhonghua Yu Fang Yi Xue Za Zhi 1987 Mar;21(2):90-1

[Studies on the DNA and RNA content of the heart, liver and kidney of rats with chronic fluorosis]

[Article in Chinese]

Guan ZZ.

PMID: 2443321 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2823909&dopt=Abstract

Biochim Biophys Acta 1987 Dec 10;931(3):262-6

Fluoride-mediated activation of guinea pig neutrophils.

Toper R, Aviram A, Aviram I.

Department of Biochemistry, Tel-Aviv University, Israel.

In guinea pig peritoneal neutrophils NaF at a concentration of above 5 mM elicited a dose-dependent, delayed and sustained activation of NADPH oxidase. Unlike in human neutrophils, in guinea pig cells, this response was independent of extracellular calcium. Fura2 fluorescence measurements indicated also a fluoride-mediated moderate elevation in the level of cytosolic calcium concentration. Pretreatment of neutrophils with pertussis toxin, blocked fluoride-promoted activation of NADPH oxidase, indicating that NaF stimulation was mediated by a G protein which is a pertussis toxin substrate. NaF-elicited calcium elevation was insensitive to the toxin. Upon transfer of NaF-stimulated cells to a fluoride-free medium, superoxide release declined and calcium levels diminished. The response of the deactivated, fluoride-prestimulated guinea pig neutrophils to a secondary stimulation with phorbol myristate acetate (PMA) or fMet-Leu-Phe, was either unaffected by the previous challenge with NaF (PMA) or augmented by it (the chemotactic peptide). In parallel to the activation of NADPH oxidase, NaF also induced translocation of protein kinase C to cell membranes. This effect was also abolished by a pretreatment with pertussis toxin.

PMID: 2823909 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3102959&dopt=Abstract

Mutat Res 1987 Mar;187(3):165-80

Mutagenic activity of fluorides in mouse lymphoma cells.

Caspary WJ, Myhr B, Bowers L, McGregor D, Riach C, Brown A.

The L5178Y mouse lymphoma cell forward-mutation assay was used to test for the mutagenic activity of sodium and potassium fluoride at the thymidine kinase locus. Mutants were detected by colony formation in soft agar in the presence of trifluorothymidine. Mutagenic and toxic responses were observed in the concentration range of 300-600 micrograms/ml with both sodium and potassium fluoride. Approximately 3-fold increases in mutant frequency were observed for concentrations in the 500-700 micrograms/ml range that reduced the relative total growth to approximately 10% in the absence or presence of a rat-liver S9 activation system. A sample of 30% sodium fluoride-70% sodium bifluoride (NaHF2) induced a similar mutagenic response but was more toxic with respect to the fluoride concentration. A specificity for fluoride ions in causing mutagenesis was indicated by the fact that much higher concentrations of sodium or potassium chloride were necessary to cause toxicity and increases in the mutant frequency. The possible involvement of chromosomal changes was signaled by the predominant increase in the small colony class of mutants.

PMID: 3102959 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3114629&dopt=Abstract

Mutat Res 1987 Sep;189(1):47-58

Extrapolation from in vitro tests to human risk: experience with sodium fluoride clastogenicity.

Scott D, Roberts SA.

Genotoxic effects observed in vitro, only at high doses or high levels of cytotoxicity, will be false positives if such conditions are not achieved or cannot be tolerated in vivo. However, for such effects to be disregarded there must be a threshold dose or level of cytotoxicity below which genotoxicity is absent. Sodium fluoride (NaF) has previously been shown to be clastogenic in vitro in Syrian hamster cells and human fibroblasts. We have extended these studies in human fibroblasts and included a positive control (mitomycin C, MMC) which is clastogenic in vivo and carcinogenic, and a chemically related control (NaCl). Cytotoxicity was measured as mitotic inhibition and cell death (loss of clonogenicity). The results are used to illustrate the problems associated with quantitative extrapolation from in vitro tests to human risk, as follows.
(1) There appears to be a threshold response (clastogenicity vs. dose) with NaF at around 10 micrograms/ml (48 h exposure) but a more definitive conclusion must await elucidation of the mechanisms of clastogenicity.
(2) NaCl is weakly clastogenic at 1000 times the threshold dose for NaF. The mechanisms are unlikely to be similar.
(3) No clastogenicity was detected with NaF below about 30% mitotic inhibition but the relationship between clastogenicity and mitotic inhibition was similar for NaF and MMC.
(4) There was no obvious threshold in the relationship between clastogenicity and cell killing with NaF. MMC was less clastogenic than NaF at equitotoxic doses. Observations 3 and 4 preclude the possibility of regarding the clastogenicity of NaF as a false positive by virtue of associated cytotoxicity.

PMID: 3114629 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2824607&dopt=Abstract

J Immunol 1987 Nov 15;139(10):3463-9

Aluminum fluoride induces phosphatidylinositol turnover, elevation of cytoplasmic free calcium, and phosphorylation of the T cell antigen receptor in murine T cells.

O'Shea JJ, Urdahl KB, Luong HT, Chused TM, Samelson LE, Klausner RD.

Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892.

Antigen activation of murine T lymphocytes leads to phosphorylation of three subunits of the murine T cell antigen receptor (L.E. Samelson, M.D. Patel, A.M. Weissman, J.B. Harford, and R.D. Klausner. 1986. Cell 46:1083). Two kinases are activated in this process: protein kinase C which leads to phosphorylation of the gamma and, to a lesser extent, the epsilon subunits on serine residues and a tyrosine kinase which phosphorylates the p21 subunit (M.D. Patel, L.E. Samelson, and R.D. Klausner. 1987. J. Biol Chem. 262:5831). We sought to determine whether treatment of these cells with NaF could simulate any of these antigen-induced events. Indeed NaF treatment resulted in breakdown of polyphosphoinositides and production of phosphoinositols. This treatment also resulted in a rise in cytosolic free Ca2+. EGTA failed to block this rise suggesting that NaF liberated intracellular stores of Ca2+. Finally NaF treatment resulted in phosphorylation of the gamma and epsilon chains of the T cell receptor indistinguishable from the effects of phorbol esters. The NaF effect was potentiated by addition of A1Cl3 consistent with the view that the active moiety is A1F4-. The A1F4--induced phosphorylations were abolished in cells in which protein kinase C was depleted by prior treatment with phorbol myristate acetate. All of these observations are compatible with the interpretation that the A1F4- phosphorylation is mediated by protein kinase C. Antigen and anti-receptor antibody-induced receptor serine phosphorylation and phophatidylinositol turnover are blocked by raising intracellular levels of cyclic adenosine monophosphate. In contrast, A1F4--induced effects were insensitive to cyclic adenosine monophosphate.

PMID: 2824607 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2826123&dopt=Abstract

EMBO J 1987 Oct;6(10):2907-13

Fluoride complexes of aluminium or beryllium act on G-proteins as reversibly bound analogues of the gamma phosphate of GTP.

Bigay J, Deterre P, Pfister C, Chabre M.

Laboratoire de Biophysique Moleculaire et Cellulaire, (Unite Associee 520 du CNRS), D.R.F.-C.E.N.G., Grenoble, France.

Fluoride activation of G proteins requires the presence of aluminium or beryllium and it has been suggested that AIF4- acts as an analogue of the gamma-phosphate of GTP in the nucleotide site. We have investigated the action of AIF4- or of BeF3- on transducin (T), the G protein of the retinal rods, either indirectly through the activation of cGMP phosphodiesterase, or more directly through their effects on the conformation of transducin itself. In the presence of AIF4- or BeF3-, purified T alpha subunit of transducin activates purified cyclic GMP phosphodiesterase (PDE) in the absence of photoactivated rhodopsin. Activation is totally reversed by elution of fluoride or partially reversed by addition of excess T beta gamma. Activation requires that GDP or a suitable analogue be bound to T alpha: T alpha-GDP and T alpha-GDP alpha S are activable by fluorides, but not T alpha-GDP beta S, nor T alpha that has released its nucleotide upon binding to photoexcited rhodopsin. Analysis of previous works on other G proteins and with other nucleotide analogues confirm that in all cases fluoride activation requires that a GDP unsubstituted at its beta phosphate be bound in T alpha. By contrast with alumino-fluoride complexes, which can adopt various coordination geometries, all beryllium fluoride complexes are tetracoordinated, with a Be-F bond length of 1.55 A, and strictly isomorphous to a phosphate group. Our study confirms that fluoride activation of transducin results from a reversible binding of the metal-fluoride complex in the nucleotide site of T alpha, next to the beta phosphate of GDP, as an analogue of the gamma phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

PMID: 2826123 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3028538&dopt=Abstract

Blood 1987 Mar;69(3):859-66

Sodium fluoride mimics effects of both agonists and antagonists on intact human platelets by simultaneous modulation of phospholipase C and adenylate cyclase activity.

Kienast J, Arnout J, Pfliegler G, Deckmyn H, Hoet B, Vermylen J.

Using intact human platelets, we studied the effect of sodium fluoride (NaF) on platelet aggregation and release reaction and correlated the functional changes to intracellular events specific for either agonist-induced or antagonist-induced platelet responses. At lower concentrations, with a peak activity between 30 and 40 mmol/L, NaF induced aggregation and release of adenosine 5'-triphosphate (ATP) that was associated with increased formation of inositol phosphates, a rise in cytosolic free Ca2+, and phosphorylation of 20-kd and 40-kd proteins. At NaF concentrations greater than 40 mmol/L, aggregation and ATP release decreased dose-dependently in parallel with a decrease in Ca2+ mobilization, whereas neither inositol phosphate formation nor 40-kd protein phosphorylation was reduced. At these concentrations, NaF caused a dose-dependent transient rise in platelet cyclic adenosine 3',5'-monophosphate (cAMP) levels that was sufficient to account for the observed reduction in Ca2+ mobilization, aggregation, and ATP release. Stimulated cAMP levels started declining rapidly within 30 seconds of addition of NaF, however. Similarly, prostacyclin (PGI2)-induced cAMP accumulation was temporarily enhanced but subsequently suppressed by NaF, suggesting either stimulation of a cAMP phosphodiesterase or delayed inhibition of adenylate cyclase. Evidence for the latter was provided by the finding that NaF pretreatment of platelets resulted in partial inhibition of PGI2-stimulated cAMP formation in the presence of the cAMP phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (MIX). We conclude that NaF exerts a dual (stimulatory and inhibitory) effect on adenylate cyclase in intact platelets that is accompanied by simultaneous activation of a phosphoinositide-specific phospholipase C; in addition, a cAMP phosphodiesterase may be activated.

PMID: 3028538 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3029057&dopt=Abstract

J Biol Chem 1987 Feb 15;262(5):1977-83

Coupling between phosphoinositide breakdown and early mitogenic events in fibroblasts. Studies with fluoroaluminate, vanadate, and pertussis toxin.

Paris S, Chambard JC, Pouyssegur J.

In the preceding paper (Paris, S., and Pouyssegur J. (1987) J. Biol. Chem. 262, 1970-1976), AlF4- and vanadate have been shown to induce inositol phosphate formation in resting hamster fibroblasts (CCL39). In this study, we show that these two phosphate analogs are good tools to explore the causal relationship between phosphoinositide breakdown and early mitogenic events. AlF4- can activate, very similarly to the mitogen alpha-thrombin: the amiloride-sensitive Na+/H+ antiport, the bumetanide-sensitive Na+/K+/Cl- co-transport, and the expression of c-myc mRNA. The link between phospholipase C activation and these early events of the mitogenic response is demonstrated by the similarity of all dose-response curves for NaF and AlCl3 and by the common sensitivity of the four events to pertussis toxin. Vanadate likewise stimulates the Na+/H+ antiport through a pertussis toxin-sensitive pathway. On longer incubations, both fluoride and vanadate were found to be toxic and failed to induce DNA synthesis. Therefore, we have used pertussis toxin to investigate the link between phospholipase C activation and commitment to DNA synthesis. We show that pertussis toxin strikingly inhibits thrombin-induced reinitiation of DNA synthesis but does not affect the stimulation by the epidermal or fibroblast growth factors, two mitogens that do not stimulate phosphoinositide breakdown in CCL39 cells. In conclusion, these studies demonstrate that activation of phospholipase C, if not an obligatory step in the action of all growth factors, plays a crucial role in the mitogenic signaling pathway of alpha-thrombin.

PMID: 3029057 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3029056&dopt=Abstract

J Biol Chem 1987 Feb 15;262(5):1970-6

Further evidence for a phospholipase C-coupled G protein in hamster fibroblasts. Induction of inositol phosphate formation by fluoroaluminate and vanadate and inhibition by pertussis toxin.

Paris S, Pouyssegur J.

We have previously reported that alpha-thrombin induces in resting hamster fibroblasts (CCL39) the formation of inositol phosphates (IP) by activating a GTP-binding protein (G protein) sensitive to pertussis toxin (Paris, S., and Pouyssegur, J. (1986) EMBO J. 5, 55-60). Here we show that IP formation in CCL39 cells can also be induced by NaF with AlCl3 and by vanadate. In the presence of Li+, IP accumulation is linear over 30 min with no detectable lag and is concentration-dependent. NaF alone is slightly stimulatory, but a marked potentiation is observed in the presence of AlCl3, by itself without effect. Maximal stimulation is obtained with 10 mM NaF and 3 microM AlCl3, and with vanadate half-maximal effect is achieved at 0.3 mM. Both stimulations are markedly inhibited (up to 80%) by pertussis toxin (half-maximal inhibition at 1-2 ng/ml). We therefore conclude that phospholipase C is stimulated by NaF plus AlCl3 (presumably acting as AlF-4) and by vanadate by direct activation of the regulatory G protein. In addition, NaF inhibits the inositol-1-phosphatase, but this effect is not potentiated by AlCl3. Similarly, vanadate inhibits inositol trisphosphate degradation. Maximal stimulations of phospholipase C by AlF-4 and vanadate are not additive, whereas they are both additive with thrombin effects. Pretreatment of cells for 15 min with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate nearly completely abolishes induction of IP formation by AlF-4 and vanadate, suggesting that protein kinase C exerts a feedback negative control either on the G protein or on phospholipase C itself. An increase in cellular cyclic AMP similarly results in a marked attenuation of AlF-4-induced IP formation, indicating that activation of phospholipase C can be controlled also by cyclic AMP. However, the stimulatory effect of AlF-4 on phospholipase C is clearly dissociated from its effect on the adenylate cyclase system.

PMID: 3029056 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3036062&dopt=Abstract

Biochem J 1987 Jan 15;241(2):409-14

Fluoroaluminates mimic guanosine 5'-[gamma-thio]triphosphate in activating the polyphosphoinositide phosphodiesterase of hepatocyte membranes. Role for the guanine nucleotide regulatory protein Gp in signal transduction.

Cockcroft S, Taylor JA.

Fluoride and guanosine 5'-[gamma-thio]triphosphate (GTP gamma S) both activate the hepatocyte membrane polyphosphoinositide phosphodiesterase (PPI-pde) in a concentration-dependent manner. AlCl3 enhances the fluoride effect, supporting the concept that [A1F4]- is the active species. Analysis of the products of inositol lipid hydrolysis demonstrate that phosphatidylinositol bisphosphate is the major lipid to be hydrolysed. Guanosine 5'-[beta-thio]diphosphate (GDP beta S) is an inhibitor of activation of PPI-pde by both fluoride and GTP gamma S. These observations suggest that the guanine nucleotide regulatory protein (termed Gp) bears a structural resemblance to the well-characterized G-proteins of the adenylate cyclase system and the cyclic GMP phosphodiesterase system in phototransduction.

PMID: 3036062 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2829237&dopt=Abstract

Prostaglandins Leukot Med 1987 Oct;29(2-3):129-39

Fluoride but not phorbol esters stimulate rat urinary bladder prostanoid synthesis: investigations into the roles of G proteins and protein kinase C.

Jeremy JY, Dandona P.

Department of Chemical Pathology and Human Metabolism, Royal Free Hospital and School of Medicine, London, U.K.

The role of G proteins and protein kinase C in mediating muscarine receptor-linked prostanoid synthesis by the rat urinary bladder was investigated using the G protein activator, sodium fluoride (NaF); the protein kinase C activators, phorbol myristate (PMA) and phorbol dibutyrate (PDBU); the protein kinase C inhibitor, H7, and the parasympathomimetic, carbachol. NaF stimulated in vitro rat urinary bladder prostacyclin (PGI2) synthesis (EC50 = 6 mmol.l-1), an action inhibited by the presence of EDTA (10 mmol.l-1). Carbachol potentiated the stimulatory action of NaF. NaF (10 mmol.l-1)-stimulated PGI2 synthesis was inhibited by the calcium channel blockers verapamil, nifedipine and the protein kinase C inhibitor, H7, in concentration-dependent manners. Carbachol-stimulated PGI2 synthesis was also inhibited by H7. PDBU and PMA were without effect on de novo, NaF- or carbachol-stimulated urinary bladder PGI2 synthesis. Other prostanoids (PGF2 and PGF2 alpha) were stimulated to the ame degree as PGI2 by NaF, and inhibited equally by H7 and calcium channel blockers. Dibutyryl adenosine 3':5'-cyclic monophosphate was without effect on de novo or NaF-stimulated prostanoid synthesis. Since fluoride activates G proteins, these data indicate that:
(1) muscarine receptor-prostanoid synthesis coupling is mediated by G proteins in the rat urinary bladder;
(2) fluoride action is mediated by protein kinase C and not adenyl cyclase, probably through activation of phospholipase C and therefore the generation of the protein kinase C activator, diacyl glycerol;
(3) activated protein kinase C may initiate Ca2++ mobilisation linked to prostanoid synthesis; and
(4) the lack of effect of the phorbol esters on urinary bladder PGI2 synthesis, in contrast to that on other smooth muscle, indicates that in different smooth muscle tissues there are varying forms of protein kinase C.

PMID: 2829237 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3040107&dopt=Abstract

Biochim Biophys Acta 1987 Sep 4;921(1):67-74

A distinction in vitro between rat liver phosphatidate phosphatase and phospholipase C.

Lamb RG, Foster K, McGuffin M.

Hepatocellular membranes (1000 X g) containing membrane-associated, labeled phosphatidic acid were incubated (1-30 min) with 2 mM oleate or 5 mM bromobenzene in the presence or absence of various metals and NaF. Under the appropriate incubation conditions, membranes displayed rapid and significant oleate- and bromobenzene-dependent increases in the dephosphorylation of labeled phosphatidic acid. However, oleate and bromobenzene activated the dephosphorylation of phosphatidate by phosphatidate phosphatase and phospholipase C, respectively. This conclusion is supported by the observation that the phosphatase stimulated by oleate is:
(1) Mg2+ -dependent;
(2) inhibited by other metals, such as Ca2+;
(3) inhibited by NaF;
(4) specific for phosphatidic acid; and
(5) associated with a rise in liver cell triacylglycerol production.
Bromobenzene, however, activated a phospholipase C that is:
(1) stimulated by various metals, such as Mg2+, Ca2+ and Ba2+;
(2) insensitive to NaF;
(3) associated with the degradation of various membrane phospholipids;
(4), associated with liver cell injury; and
(5) not associated with a rise in liver cell triacylglycerol formation.
These results suggest that under appropriate conditions in vitro the dephosphorylation of phosphatidic acid can be used to assess changes in phosphatidate phosphatase and/or phospholipase C activity. The distinction between these enzymes is important, since phosphatidate phosphatase and phospholipase C regulate key steps in phospholipid biosynthesis and degradation, respectively.

PMID: 3040107 [PubMed - indexed for MEDLINE


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2820087&dopt=Abstract

Toxicol Lett 1987 Sep;38(1-2):169-76

Sodium fluoride produces a K+ efflux by increasing intracellular Ca2+ through Na+-Ca2+ exchange.

McIvor ME, Cummings CC.

Acute fluoride intoxication increases intracellular calcium (Cai), manifested by increased twitch tension in cardiac muscle, and by potassium efflux (mediated by Ca2+-dependent K+ channels) in fluoridated erythrocytes. Fluoride, like isoproterenol, stimulates adenylate cyclase, and could increase Cai via the effects of cAMP on Ca2+ channels. However, while the inotropic effects of fluoride mimicked isoproterenol in rat atria, their effects on the time course of isometric contraction were quite different. In addition, acetylcholine negated isoproterenol's effect on twitch tension but did not modulate the effects of fluoride. Further, the Ca2+ channel antagonist verapamil had no effect on fluoride-stimulated K+ efflux from erythrocytes. Fluoride also inhibits Na+-K+ ATPase, and increases intracellular Na+, so could increase Cai via Na+-Ca2+ exchange. Lanthanum, which blocks Na+-Ca2+ exchange, blocks fluoride-induced K+ efflux in erythrocytes. We conclude that the effects of fluoride on adenylate cyclase are not important in intact tissue, and that inhibition of Na+-K+ ATPase and subsequent Na2+-Ca2+ exchange may be the mechanism of increased Cai in acute fluoride toxicity.

PMID: 2820087 [PubMed - indexed for MEDLINE]


http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3623074&dopt=Abstract

Gen Comp Endocrinol 1987 Aug;67(2):178-88

Basal and stimulated adenylate cyclase activity in the gill epithelium of the rainbow trout.

Guibbolini M, Lahlou B.

Basal and stimulated adenylate cyclase specific activity was characterized in gill plasma membrane of freshwater-adapted trout by measuring the conversion of [alpha-32P]ATP into [alpha-32P]cyclic AMP. Both basal and isoproterenol- or sodium fluoride-stimulated enzyme activities were linear with time and protein concentration. The optimum activities were obtained using a pH buffer of 7.5 and a temperature of 20 degrees. The Km for ATP was 0.5 mM in the presence or absence of the stimulators. The presence of 10(-5) M guanosine-5'-triphosphate and 4 X 10(-3) M MgCl2 (2.41 X 10(-3) M free Mg2+) was required to optimize not only the basal activity but also the stimulation ratio (test/control) produced by these agents. On the contrary, Ca2+ was inhibitory. IC50 for CaCl2 was 5 X 10(-4) M (10(-7) M free Ca2+) in the presence or absence of the stimulators. Under these conditions, the basal adenylate cyclase specific activity was 400-450 pmol/mg protein/10 min. A maximal stimulation was produced by isoproterenol or PGE1 10(-5) M (50% increase over basal activity) or by glucagon 5.7 X 10(-10) M (30%). In addition, this enzyme displayed high sensitivity to sodium fluoride which induced a particularly large maximal effect (370%) at a concentration of 10(-2) M.

PMID: 3623074 [PubMed - indexed for MEDLINE]


NOTE: AG Gilman, co-author of this report, shared the 1994 Nobel Prize for the discovery of "G-proteins and the role of these proteins in signal transduction in cells."

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3100518&dopt=Abstract

J Biol Chem 1987 Jan 15;262(2):752-6

The effect of activating ligands on the intrinsic fluorescence of guanine nucleotide-binding regulatory proteins.

Higashijima T, Ferguson KM, Sternweis PC, Ross EM, Smigel MD, Gilman AG.

The intensity of the tryptophan fluorescence of the alpha subunits of guanine nucleotide-binding regulatory proteins increases when they bind guanosine 5'-O-(3-thio)triphosphate (GTY gamma S). The kinetics of the fluorescence enhancement and of the measured binding of [35S]GTP gamma S are well correlated. The addition of Mg2+ to the nucleotide-bound proteins causes a further, rapid increase in the fluorescence intensity. Similar effects result from exposure of the proteins to F- and Mg2+, and the required concentration of F- is reduced by the inclusion of Al3+. It is presumed that the more highly fluorescent state of the G protein alpha subunits represents their active conformation.

PMID: 3100518 [PubMed - indexed for MEDLINE]


NOTE: AG Gilman, co-author of this report, shared the 1994 Nobel Prize for the discovery of "G-proteins and the role of these proteins in signal transduction in cells."

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3112160&dopt=Abstract

J Biol Chem 1987 Aug 15;262(23):11375-81

Expression of cDNAs for G proteins in Escherichia coli. Two forms of Gs alpha stimulate adenylate cyclase.

Graziano MP, Casey PJ, Gilman AG.

Complementary DNAs that encode two forms of the alpha subunit (Gs alpha) of the guanine nucleotide-binding protein responsible for stimulation of adenylate cyclase (Gs) have been inserted into plasmid vectors for expression in Escherichia coli. Following transformation of either of these plasmids into E. coli K38, Gs alpha accumulates to 0.4-0.8 mg/liter (approximately 0.1% of total protein), as judged by immunoblot analysis with specific antisera. Based on deduced amino acid sequence, the two cDNAs should encode proteins with molecular weights of 44,500 and 46,000, respectively (Robishaw, J.D., Smigel, M. D., and Gilman, A. G. (1986) J. Biol. Chem. 261, 9587-9590). Expression of these cDNAs in E. coli yields proteins that co-migrate on sodium dodecyl sulfate-polyacrylamide gels with the Gs alpha subunits from S49 lymphoma cell membranes, with apparent molecular weights of 45,000 and 52,000, respectively. Low levels of activity are detected in the 100,000 X g supernatant after lysis and fractionation of E. coli expressing either form of Gs alpha. Partial purification of Gs alpha from E. coli lysates yields preparations in which significant and stable activity can be assayed. Both forms of Gs alpha migrate through sucrose gradients as soluble, monodisperse species in the absence of detergent. As expressed in E. coli, both forms of Gs alpha can reconstitute isoproterenol-, guanine nucleotide-, and fluoride-stimulated adenylate cyclase activity in S49 cyc-cell membranes to approximately the same degree and can be ADP-ribosylated with [32P]NAD+ and cholera toxin. However, based on the specific activity of purified rabbit liver Gs, only 1-2% of the Gs alpha expressed in E. coli appears to be active. Incubation of partially purified fractions of recombinant Gs alpha with guanosine 5'-(3-O-thio)triphosphate and resolved beta gamma subunits isolated from purified bovine brain G proteins results in a 7-10-fold increase in Gs activity. Incubation of bovine brain beta gamma with recombinant Gs alpha also leads to a dramatic increase in observed levels of cholera toxin-catalyzed [32P]ADP-ribosylation.

PMID: 3112160 [PubMed - indexed for MEDLINE]


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