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At least 469 records · Page 26Linked to original sources
PubMed2005

Inhibition [corrected] of olfactory receptor neuron input to olfactory bulb glomeruli mediated by suppression of presynaptic calcium influx.

We investigated the cellular mechanism underlying presynaptic regulation of olfactory receptor neuron (ORN) input to the mouse olfactory bulb using optical-imaging techniques that selectively report activity in the ORN presynaptic terminal. First, we loaded ORNs with calcium-sensitive dye and imaged stimulus-evoked calcium influx in a slice preparation. Single olfactory nerve shocks evoked rapid fluorescence increases that were largely blocked by the N-type calcium channel blocker omega-conotoxin GVIA. Paired shocks revealed a long-lasting suppression of calcium influx with approximately 40% suppression at 400-ms interstimulus intervals and a recovery time constant of approximately 450 ms. Blocking activation of postsynaptic olfactory bulb neurons with APV/CNQX reduced this suppression. The GABA(B) receptor agonist baclofen inhibited calcium influx, whereas GABA(B) antagonists reduced paired-pulse suppression without affecting the response to the conditioning pulse. We also imaged transmitter release directly using a mouse line that expresses synaptopHluorin selectively in ORNs. We found that the relationship between calcium influx and transmitter release was superlinear and that paired-pulse suppression of transmitter release was reduced, but not eliminated, by APV/CNQX and GABA(B) antagonists. These results demonstrate that primary olfactory input to the CNS can be presynaptically regulated by GABAergic interneurons and show that one major intracellular pathway for this regulation is via the suppression of calcium influx through N-type calcium channels in the presynaptic terminal. This mechanism is unique among primary sensory afferents.

2-Amino-5-phosphonovalerate↗
PubMed2002

Gamma-aminobutyric acid-induced calcium signalling in rat superior collicular neurones.

Ionotropic gamma-aminobutyric acid (GABA) receptors are known to mediate excitation in neonatal neurones as a crucial developmental factor. In the present study we employed calcium imaging techniques with the calcium indicator Fura-2-AM to study the pharmacology of GABA-induced calcium responses in cultures prepared from neonatal rat superficial superior colliculus (SC), after immunocytochemical labelling confirmed the presence of GABA(C) rho(1) subunits in 35% of neurones. Rises in neuronal intracellular calcium were obtained in response to GABA and also to the subtype-specific GABA(A) agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol. However, the GABA(C) agonist cis-4-aminocrotonic acid induced calcium response only at unspecifically high concentrations (500 microM). Co-application of GABA antagonists revealed that both GABA(A&C) agonists' actions could be blocked by the GABA(A) antagonist bicuculline but not the GABA(C) antagonists 1,2,5,6-tetrahydro-(pyridin-4-yl) methylphosphinic acid. This suggests that activation of GABA(A) but not GABA(C) receptors contributes to excitatory GABA responses and related calcium signals in neonatal SC neurones.

Animals↗
PubMed2004

Convergence of excitatory and inhibitory hair cell transmitters shapes vestibular afferent responses.

The vestibular semicircular canals respond to angular acceleration that is integrated to angular velocity by the biofluid mechanics of the canals and is the primary origin of afferent responses encoding velocity. Surprisingly, some afferents actually report angular acceleration. Our data indicate that hair-cell/afferent synapses introduce a mathematical derivative in these afferents that partially cancels the biomechanical integration and results in discharge rates encoding angular acceleration. We examined the role of convergent synaptic inputs from hair cells to this mathematical differentiation. A significant reduction in the order of the differentiation was observed for low-frequency stimuli after gamma-aminobutyric acid type B receptor antagonist administration. Results demonstrate that gamma-aminobutyric acid participates in shaping the temporal dynamics of afferent responses.

Acceleration↗
PubMed2003

Four week feeding toxicity study with phenylphosphinic acid in rats.

Phenylphosphinic acid was fed in graded concentrations of either 0 (control), 100, 1,000, or 10,000 ppm to rats for 28 days. These concentrations provided average daily doses of 8, 76, and 779 mg/kg (males) and 9, 83, and 859 mg/kg (females). No signs of adverse response were detected at any concentration up to the highest levels tested, 10,000 ppm or 779 (male) or 859 (female) mg/kg. Parameters measured were clinical signs, growth, neurobehavior, ophthalmology, and clinical and anatomical pathology. Phenylphosphinic acid is very low in toxicity following 31 days of feeding to the rat.

Animals↗
PubMed2002

Tunable ligands for asymmetric catalysis: readily available carbohydrate-derived diarylphosphinites induce high selectivity in the hydrovinylation of styrene derivatives.

Only a limited number of ligands have been successfully employed for the Ni-catalyzed asymmetric hydrovinylation reaction. Diarylphosphonites prepared from readily available carbohydrates in conjunction with a highly dissociated counterion ([3,5-(CF3)2-C6H3)4B]- or SbF6-) effect the hydrovinylation of 4-bromostyrene or 4-isobutylstyrene under ambient pressure of ethylene with the best overall selectivities reported to date for these important substrates. In a prototypical synthesis of a 2-arylpropionic acid, 3-(4-bromophenyl)-1-butene (prepared in 98% isolated yield and 89% ee from 4-bromostyrene) has been transformed into (R)-ibuprofen by Ni-catalyzed cross-coupling with i-BuMgBr, ozonolysis, and subsequent oxidation of the resulting aldehyde.

Carbohydrates↗
PubMed2005

Detection of phosphorus oxyanions in synthetic geothermal water using ion chromatography-mass spectrometry techniques.

Recent developments in microbiology suggest that reduced inorganic phosphorus oxyanions, including hypophosphite and phosphite, may be present in nature. These studies have inspired the development of specific and sensitive methods that detect phosphorus oxyanions in natural water. This paper will discuss a new technique that couples suppressed conductivity ion chromatography (Dionex AS17 analytical column and potassium hydroxide eluent) with electrospray mass spectrometry (IC/MS) with limits of detection nearly 200 times lower than those reported using suppressed conductivity detection. The technique was optimized for the detection of hypophosphite, phosphite, and phosphate in a synthetic geothermal water matrix. Samples were pre-treated with silver and sulfonic acid cartridges, and injection loop sizes as large as 800microl were employed to enhance instrument sensitivity. All peaks were clearly resolved, and calibrations were linear with estimated 3sigma limits of detection of 0.011, 0.0020, and 0.029microM for hypophosphite, phosphite, and phosphate, respectively.

Chromatography, Ion Exchange↗
PubMed2006

Processing of rayon waste effluent for the recovery of zinc and separation of calcium using thiophosphinic extractant.

Zinc is used in various metallurgical, chemical and textile industries. In textile industries, waste effluent containing zinc is generated during the manufacture of rayon yarn. Due to the strict environmental regulations and the presence of toxic metallic and other constituents, the discharge of effluents in sewage is restricted. In view of above a process has been developed for the recovery of zinc from rayon waste effluent following solvent extraction technique using thiophosphinic extractants Cyanex 272 and 302. Before recycling of zinc sulphate solution in spinning bath, solution must be free from calcium, which is deleterious to the process as gypsum precipitates and forms scale. The extractant Cyanex 302 has been found selective for the recovery of 99.99% of zinc in the form of [R(2)Zn](org) from the effluent above equilibrium pH 3.4 maintaining the O/A ratio of 1/30 leaving all the calcium in the raffinate. The zinc from the loaded Cyanex 302 can be stripped with 10% sulphuric acid at even O/A ratio of 10. The stripped solution thus obtained could be recycled in the spinning bath of the rayon plant and raffinate could be disposed safely without affecting environment.

Calcium↗
PubMed1994

Isolation and characterization of hypophosphite--resistant mutants of Escherichia coli: identification of the FocA protein, encoded by the pfl operon, as a putative formate transporter.

Hypophosphite was used as a toxic analogue to identify genes whose products have a putative function in the transport of formate. Two Tn10-derived insertion mutants were identified that exhibited increased resistance to high concentrations of hypophosphite in the culture medium. The transposon was located in the identical position in the focA (formate channel; previously termed orf) gene of the pfl operon in both mutants. A defined chromosomal focA nonsense mutant, which showed minimal polarity effects on pfl gene expression, had the same phenotype as the insertion mutants. Results obtained using a hycA-lacZ fusion to monitor changes in the intracellular formate concentration in a focA mutant indicated that the level of formate inside the cell was elevated compared with the wild type. Moreover, it could be shown that there was a corresponding reduction of approximately 50% in the amount of formate excreted by a focA mutant into the culture medium. Taken together, these results indicate that formate accumulates in anaerobic cells which do not have a functional focA gene product and that one function of FocA may be to export formate from the cell. A further significant result was that hypophosphite could substitute for formate in activating hycA gene expression. This hypophosphite-dependent activation of hycA gene expression was reduced 10-fold in a focA null mutant, suggesting that hypophosphite must first enter the cell before it can act as a signal to activate hycA expression. By analogy, these data suggest that focA may also be functional in the import of formate into anaerobic Escherichia coli cells. Site-specific mutagenesis identified the translation initiation codon of focA as a GUG. Therefore, the FocA polypeptide has a molecular weight of 30,958. FocA shows significant similarity at both the primary and secondary structural levels with the NirC protein of E. coli and the FdhC protein of Methanobacterium formicicum. All three proteins are predicted to be integral membrane proteins. A detailed in vivo TnphoA mutagenesis study predicted that FocA has six membrane-spanning segments.

Acetyltransferases↗
PubMed2006

Novel palladium complexes employing mixed phosphine phosphonates and phosphine phosphinates as anionic chelating [P,O] ligands.

A route to various substituted phosphine phosphonic acid compounds of the general form Ar(2)PC(6)H(4)PO(OH)(2) (Ar = Ph, o-MeC(6)H(4), o-MeOC(6)H(4)) has been investigated. These compounds were employed as bidentate anionic [P,O] ligands in neutral palladium complexes. The [P,O] chelating coordination was determined by X-ray crystallography of a representative palladium complex. Furthermore, the bifunctional ligand Ph(2)PC(6)H(4)PO(OH)Ph represents the first example of a chelating anionic [P,O] ligand resulting from the combination of a phosphine and a phosphinate moiety.

Journal Article↗
PubMed2004

Synthesis and evaluation of aminophosphinic acid derivatives as inhibitors of renal dipeptidase.

Renal dipeptidase (RDP) is an enzyme overexpressed in benign and malignant colorectal tumors. In an effort to identify potent inhibitors of this enzyme, a series of aminophosphinic acid derivatives were synthesized. Compounds 3a and 3c in which the phenyl ring was para substituted with F and Br and olefin with Z geometry, showed better inhibitory activity against RDP enzyme (IC50 = 5-6 nM).

Alkenes↗
PubMed2000

GABAC receptor sensitivity is modulated by interaction with MAP1B.

GABA(C) receptors contain rho subunits and mediate feedback inhibition from retinal amacrine cells to bipolar cells. We previously identified the cytoskeletal protein MAP1B as a rho1 subunit anchoring protein. Here, we analyze the structural basis and functional significance of the MAP1B-rho1 interaction. Twelve amino acids at the C terminus of the large intracellular loop of rho1 (and also rho2) are sufficient for interaction with MAP1B. Disruption of the MAP1B-rho interaction in bipolar cells in retinal slices decreased the EC(50) of their GABA(C) receptors, doubling the receptors' current at low GABA concentrations without affecting their maximum current at high concentrations. Thus, anchoring to the cytoskeleton lowers the sensitivity of GABA(C) receptors and provides a likely site for functional modulation of GABA(C) receptor-mediated inhibition.

Amino Acid Transport Systems, Neutral↗
PubMed1992

The formation and properties of metal oxide poly(vinylphosphonic acid) cements.

Aqueous solutions of poly(vinylphosphonic acid) have been found to form polyelectrolyte cements with a wide range of metal oxides. Poly(vinylphosphonic acid), PVPA, has a structure similar to that of poly(acrylic acid), PAA, but contains pendant phosphonic acid,--P(O)(OH)2, groups in place of the carboxylic acid,--COOH, groups of the zinc polycarboxylate, and glass polyalkenoate cements. It is a stronger acid than PAA, with a greatly increased reactivity toward metal oxides. The physical and mechanical properties of a number of metal oxide PVPA cements were studied and compared with those of zinc polycarboxylate cements. The faster acting of the metal oxide PVPA cement seems to produce a cement that is less susceptible to early hydrolysis.

Dental Cements↗
PubMed1998

GABA(C) receptor antagonists differentiate between human rho1 and rho2 receptors expressed in Xenopus oocytes.

The selective GABA(C) receptor antagonist, (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA), is eight times more potent against human recombinant p receptors than p2 receptors expressed in Xenopus oocytes. (3-Aminopropyl)methylphosphinic acid (CGP35024), the methylphosphinic acid analogue of GABA, and [(E)-3-aminopropen-1-yl]methylphosphinic acid (CGP44530), an open chain analogue of TPMPA, were five and four times, respectively, more potent as antagonists of p1 receptors than as antagonists of p2 receptors. Isoguvacine was a weak partial agonist at both p1 and p2 receptors with intrinsic activities (calculated as a percentage of the maximum whole cell current produced by a maximum dose of GABA) of 45 and 68%, respectively, of the maximum response produced by GABA. In agreement with other workers, it was found that imidazole-4-acetic acid was a partial agonist at both p1 and p2 receptors, showing higher intrinsic activity at p2 than at p1 receptors. The p1 receptor antagonist, trans-4-amino-2-methylbut-2-enoic acid (2-MeTACA), was a partial agonist at p2 receptors with an intrinsic activity of 34%. 2-MeTACA may be useful in differentiating between homo-oligomeric p1 and p2 receptors in native systems. These studies reveal significant differences in the antagonist profile of human recombinant p1 and p2 GABA(C) receptors.

Animals↗
PubMed2003

GABAC receptors in the rat superior colliculus and pretectum participate in synaptic neurotransmission.

In mammals, GABA(C) receptors seem to be specifically expressed in the retina and the subcortical visual system, with highest extraretinal expression levels in the superior colliculus (SC). Although its presence in the superficial SC has been demonstrated physiologically, a direct involvement of this receptor type in fast synaptic neurotransmission still awaits verification. We addressed the question of a possible synaptic localization of GABA(C) receptors by performing in vitro whole-cell patch-clamp recordings of inhibitory postsynaptic currents (IPSCs) in single neurons of the rat SC and the neighboring pretectal nuclear complex, where GABA(C) receptors are also expressed at significant levels. To increase the likelihood to record IPSCs we induced spontaneous activity by application of the potassium channel blocker 4-aminopyridine (4-AP) and blocked glutamate-mediated excitatory neurotransmission with kynurenic acid. All 4-AP-induced postsynaptic currents were of synaptic origin because they were completely suppressed by lidocaine or by substitution of extracellular calcium with cobalt. In 40% of the SC cells and in 60% of the pretectal neurons, IPSCs in the presence of 4-AP and kynurenic acid were only partly blocked by the selective GABA(A) receptor antagonist bicuculline. Inhibitory currents that were insensitive to bicuculline, however, could be blocked by coapplication of either the specific GABA(C) receptor antagonist 1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid or picrotoxin, an unselective GABA(A) and GABA(C) receptor antagonist. We conclude that GABA(C) receptors are, at least partially, located synaptically in SC and pretectal neurons in the rat, which indicates a direct function of this receptor type for synaptic processing in both structures.

4-Aminopyridine↗
PubMed2002

[Determination of trace palladium based on kinetic-spectrophotometry with malachite green-sodium hypophosphite system].

A new kinetic-spectrophotometric method for the determination of trace amount of palladium has been proposed. It is based on the palladium catalysed discoloring reaction of malachite green reduced by sodium hypophosphite in phosphoric acid buffer solution (pH = 2.0). The linear range of determination of palladium is 0-10 microgram.L-1, the detection limit is 9.78 x 10(-11) g.mL-1. The method has been used for the determination of palladium in some catalyst with satisfactory results. The mechanism of the reaction has also been discussed.

Indicators and Reagents↗
PubMed2004

Efficient routes to epimerically-pure side-chain derivatives of lanosterol.

A technically simple route is described to individual epimers of side-chain derivatives of lanosterol (3beta-hydroxy-5alpha-lanosta-8,24-diene). Epimerically pure 24,25-epoxy-, 24,25-dihydroxy- and 24-bromo-25-hydroxy-lanosterol have been prepared in good yield from commercial (50-60%) lanosterol. Hypophosphorous acid was used as a catalyst for the cohalogenation of the Delta24(25) bond and also for the efficient conversion of 24,25-epoxy- and 24-bromo-25-hydroxylanosterol to epimerically pure 24(R) or 24(S)-24,25-dihydroxylanosterols.

Acetylation↗
PubMed2001

CGP 36216 is a selective antagonist at GABA(B) presynaptic receptors in rat brain.

In rat neocortical preparations maintained in Mg(2+)-free Krebs medium, baclofen depressed the frequency of spontaneous discharges in a concentration-dependent manner (EC(50) = 6 microM), sensitive to (3-aminopropyl)ethylphosphinic acid (CGP 36216) (100, 300 and 500 microM) (pA(2) = 3.9 +/- 0.1). By contrast, CGP 36216, up to 1 mM, was ineffective in antagonising baclofen-induced hyperpolarisations, mediated through gamma-aminobutyric acid(B) (GABA(B)) postsynaptic receptors. In electrically stimulated brain slices preloaded with [3H]GABA, CGP 36216 increased [3H]GABA release (IC(50) = 43 microM), which was reversed by baclofen (20 microM). While CGP 36216 is ineffective at GABA(B) postsynaptic receptors, it is appreciably more active at presynaptic receptors.

Animals↗