Glycine-induced long-term potentiation is associated with structural and functional modifications of α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid receptors

Global long-term potentiation (LTP) was induced in organotypic hippocampal slice cultures by a brief application of 10 mM glycine. Glycine-induced LTP was occluded by previous theta burst stimulation-induced potentiation, indicating that both phenomena share similar cellular processes. Glycine-induced LTP was associated with increased [3H]α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) binding in membrane fractions as well as increased amount of a selective spectrin breakdown product generated by calpain-mediated spectrin proteolysis. Antibodies against the C-terminal (C-Ab) and N-terminal (N-Ab) domains of GluR1 subunits were used to evaluate structural changes in AMPA receptor properties resulting from glycine-induced LTP. No quantitative or qualitative changes were observed in Western blots from membrane fractions prepared from glycine-treated slices with C-Ab. In contrast, Western blots stained with N-Ab revealed the formation of a 98-kDa species of GluR1 subunits as well as an increased amount of immunoreactivity after glycine-induced LTP. The amount of spectrin breakdown product was positively correlated with the amount of the 98-kDa species of GluR1 after glycine treatment. Functional modifications of AMPA receptors were evaluated by determining changes in the effect of pressure-applied AMPA on synaptic responses before and after glycine-induced LTP. Glycine treatment produced a significant increase in AMPA receptor function after potentiation that correlated with the degree of potentiation. The results indicate that LTP induction produces calpain activation, truncation of the C-Ab domain of GluR1 subunits of AMPA receptors, and increased AMPA receptor function. They also suggest that insertion of new receptors takes place after LTP induction.

Growth factor-mediated Fyn signaling regulates α-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor expression in rodent neocortical neurons

Src-family protein tyrosine kinases (PTKs) transduce signals to regulate neuronal development and synaptic plasticity. However, the nature of their activators and molecular mechanisms underlying these neural processes are unknown. Here, we show that brain-derived neurotrophic factor (BDNF) and platelet-derived growth factor enhance expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor 1 and 2/3 proteins in rodent neocortical neurons via the Src-family PTK(s). The increase in AMPA receptor levels was blocked in cultured neocortical neurons by addition of a Src-family-selective PTK inhibitor. Accordingly, neocortical cultures from Fyn-knockout mice failed to respond to BDNF whereas those from wild-type mice responded. Moreover, the neocortex of young Fyn mutants exhibited a significant in vivo reduction in these AMPA receptor proteins but not in their mRNA levels. In vitro kinase assay revealed that BDNF can indeed activate the Fyn kinase: It enhanced tyrosine phosphorylation of Fyn as well as that of enolase supplemented exogenously. All of these results suggest that the Src-family kinase Fyn, activated by the growth factors, plays a crucial role in modulating AMPA receptor expression during brain development.

Correlation between kinetics and RNA splicing of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in neocortical neurons.

In the cortex fast excitatory synaptic currents onto excitatory pyramidal neurons and inhibitory nonpyramidal neurons are mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors exhibiting cell-type-specific differences in their kinetic properties. AMPA receptors consist of four subunits (GluR1-4), each existing as two splice variants, flip and flop, which critically affect the desensitization properties of receptors expressed in heterologous systems. Using single cell reverse transcription PCR to analyze the mRNA of AMPA receptor subunits expressed in layers I-III neocortical neurons, we find that 90% of the GluR1-4 in nonpyramidal neurons are flop variants, whereas 92% of the GluR1-4 in pyramidal neurons are flip variants. We also find that nonpyramidal neurons predominantly express GluR1 mRNA (GluR1/GluR1-4 = 59%), whereas pyramidal neurons contain mainly GluR2 mRNA (GluR2/GluR1-4 = 59%). However, the neuron-type-specific splicing is exhibited by all four AMPA receptor subunits. We suggest that the predominance of the flop variants contributes to the faster and more extensive desensitization in nonpyramidal neurons, compared to pyramidal cells where flip variants are dominant. Alternative splicing of AMPA receptors may play an important role in regulating synaptic function in a cell-type-specific manner, without changing permeation properties.

Intracellular polyamines mediate inward rectification of Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors.

alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors that lack the glutamate receptor GluR2 subunit are Ca(2+)-permeable and exhibit inwardly rectifying current responses to kainate and AMPA. A proportion of cultured rat hippocampal neurons show similar Ca(2+)-permeable inwardly rectifying AMPA receptor currents. Inward rectification in these neurons was lost with intracellular dialysis and was not present in excised outside-out patches but was maintained in perforated-patch whole-cell recordings, suggesting that a diffusible cytoplasmic factor may be responsible for rectification. Inclusion of the naturally occurring polyamines spermine and spermidine in the recording pipette prevented loss of rectification in both whole-cell and excised-patch recordings; Mg2+ and putrescine were without effect. Inward rectification of Ca(2+)-permeable AMPA receptors may reflect voltage-dependent channel block by intracellular polyamines.

4-(2-hydroxyethyl)anilinium 3-carboxy-4-hydroxybenzenesulfonate monohydrate

In the structure of the title compound C8H12NO+ C7H5O6S- . H2O, from the reaction of 2-(4-aminophenyl)ethanol with 5-sulfosalicylic acid, the cations form head-to-tail hydrogen-bonded chains through C1/1(9) anilinium N+-H...O(hydroxyl} interactions while the anions also form similar but C1/1(8)-linked chains through carboxylic acid O-..O(sulfonate) interactions. The chains inter-associate through a number of N-H...O and O-H...O bridging interactions giving a two-dimensional array in the ab plane.

Pseudo-merohedral twinning in the structure of the hydrated 1:1 proton-transfer compound of 5-sulfosalicylic acid with 4-aminopyridine

The structure of the pseudo-merohedrally twinned crystal of the 1:1 proton-transfer compound of 5-sulfosalicylic acid (3-carboxy-4-hydroxybenzenesulfonic acid) with 4-aminopyridine: 4-aminopyridinium 3-carboxy-4-hydroxybenzenesulfonate sesquihydrate has been determined at 180 K and the hydrogen-bonding pattern is described. Crystals of the compound are monoclinic with space group P21/c, with unit cell dimensions a = 35.2589(8), b = 7.1948(1), c = 24.5851(5) Å, β = 110.373(2)o, and Z = 16. The monoclinic asymmetric unit comprises four cation-anion pairs and six water molecules of solvation with only the pyridinium cations having pseudo-symmetry as a result of inter-cation aromatic ring π-π stacking effects. Extensive hydrogen bonding gives a three-dimensional framework structure.

Hexaaquamagnesium bis(3-carboxy-4-hydroxybenzenesulfonate) dihydrate

In the structure of the title compound, [Mg(H2O)6]2+ 2(C7H5O6S-). 2(H2O), the octahedral complex cations lie on crystallographic inversion centres and are hydrogen-bonded through the coordinated waters to the substituted benzenesulfonate monoanions and the water molecules of solvation, and together with a carboxylic acid O-H...O(sulfonate) association, give a three-dimensional structure.

4-Amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide-4-nitrobenzoic acid

In the asymmetric unit of the title co-crystal, C12H14N4O2S . C7H5NO4 there are two independent but conformationally similar heterodimers, which are formed through intermolecular N-H...O(carboxy) and carboxyl O-H...N hydrogen-bond pairs, giving a cyclic motif [graph set R2/2(8)]. The dihedral angles between the rings in the sulfonamide molecules are 78.77(8) and 82.33(9)deg. while the dihedral angles between the ring and the CO2H group in the acids are 2.19(9) and 7.02(10)deg. A two-dimensional structure parallel to the ab plane is generated from the heterodimer units through hydrogen-bonding associations between NH2 and sulfone groups. Between neighbouring two-dimensional arrays there are two types of aromatic pi-pi stacking interactions involving either one of the pyrimidine rings and a 4-nitrobenzoic acid molecule [minimum ring centroid separation = 3.5886(9)A] or two acid molecules [minimum ring centroid separation = 3.7236(10)A].

4-(4-Nitrobenzyl)pyridinium 3-carboxy-4-hydroxybenzenesulfonate

In the title salt, C12H11N2O2+·C7H5O6S-, the dihedral angle between the benzene and pyridine rings in the 4-(4-nitrobenzyl)pyridinium cation is 82.7 (2)°. Within the anion there is an intramolecular hydroxy-O-HO(carboxylic acid) bond. In the crystal, the cation forms a single N+-HOsulfonate hydrogen bond with the anion. These cation-anion pairs interact through duplex anion carboxylic acid O-HOsulfonate hydrogen bonds, giving a centrosymmetric cyclic association [graph set R22(16)]. The crystals studied were non-merohedrally twinned.

The structures of the isomorphous potassium and rubidium salts of 4-nitrobenzoic acid and an overview of the metal complex stereochemistries of the alkali metal salt series with this ligand

The structures of the isomorphous potassium and rubidium polymeric coordination complexes with 4-nitrobenzoic acid, poly[mu2-aqua-aqua-mu3-(4-nitrobenzoato)-potassium], [K(C7H4N2O2)(H2O)2]n, (I) and poly[mu3-aqua-aqua-mu5-(4-nitrobenzoato)-rubidium], [Rb(C7H4N2O2)(H2O)2]n, (II) have been determined. In (I) the very distorted KO6 coordination sphere about the K+ centres in the repeat unit comprise two bridging nitro O-atom donors, a single bridging carboxyl O-atom donor and two water molecules, one of which is bridging. In the the Rb complex (II), the same basic MO6 coordination is found in the repeat unit but is expanded to RbO9 through a slight increase in the accepted Rb-O bond length range and includes an additional Rb-O(carboxyl) bond, completing a bidentate O,O'-chelate interaction, and additional bridging Rb-Onitro) and Rb-O(water) bonds. The comparative K-O and Rb-O bond length ranges are 2.738(3)-3.002(3)Ang. (I) and 2.884(2)-3.182(2)Ang. (II). The structure of (II) is also isomorphous as well as isostructural with the known structure of the nine-coordinate caesium 4-nitrobenzoate analogue, [Cs(C7H4N2O~2~)(H~2~O)2]n, (III) in which the Cs---O range is 3.047(4)-3.338(4)Ang. In all three complexes, common basic polymeric extensions are found, including two different centrosymmetric bridging interactions through both water and nitro groups as well as extensions along c through the p-related carboxyl group, giving a two-dimensional structure in (I). In (II) and (III), three-dimensional structures are generated through additional bridges through the nitro and water O-atoms. In all structures, both water molecules are involved in similar intra-polymer O-H...O hydrogen-bonding interactions to both carboxyl as well as water O-atom acceptors. A comparison of the varied coordination behaviour of the full set of Li-Cs salts with 4-nitrobenzoic acid is also made.

Crystal structures of the potassium and rubidium salts of (3,5-dichlorophenoxy)acetic acid: Two isotypic coordination polymers

The two-dimensional coordination polymeric structures of the hydrated potassium and rubidium salts of (3,5-dichlorophenoxy)acetic acid, (3,5-D) namely, poly[mu-aqua-bis[mu3-2-(3,5-dichlorophenoxy)acetato]potassium, [K2(C8H5Cl2O3)2 (H2O)]n (I) and poly[mu-aqua-bis[mu3-2-(3,5-dichlorophenoxy)acetato]dirubidium] [Rb2(C8H5Cl2O3)2 (H2O)]n (II), respectively have been determined and are described. The two compounds are isotypic and the polymer is based on centrosymmetric dinuclear bridged complex units. The irregular six-coordination about the metal centres comprises a bridging water molecule lying on a twofold rotation axis, the phenoxy O-atom donor and and a triple bridging carboxylate O-atom of the oxoacetate side chain of the 3,5-D ligand in a bidentate chelate mode, the second carboxy O-donor, also bridging. The K-O and Rb-O bond-length ranges are 2.7238(15)--2.9459(14) and 2.832(2)--3.050(2) \%A respectively and the K...K and Rb...Rb separations in the dinuclear unit are 4.0214(7) and 4.1289(6) \%A, respectively. Within the two-dimensional layers which lie parallel to (100), the coordinated water molecule forms an O---H...O hydrogen bond to the single bridging carboxylate O atom.

The three-dimensional hydrogen-bonded structures in the ammonium and sodium salt hydrates of 4-aminophenylarsonic acid

The structures of two hydrated salts of 4-aminophenylarsonic acid (p-arsanilic acid), namely ammonium 4-aminophenylarsonate monohydrate, NH4(+)·C6H7AsNO3(-)·H2O, (I), and the one-dimensional coordination polymer catena-poly[[(4-aminophenylarsonato-κO)diaquasodium]-μ-aqua], [Na(C6H7AsNO3)(H2O)3]n, (II), have been determined. In the structure of the ammonium salt, (I), the ammonium cations, arsonate anions and water molecules interact through inter-species N-H...O and arsonate and water O-H...O hydrogen bonds, giving the common two-dimensional layers lying parallel to (010). These layers are extended into three dimensions through bridging hydrogen-bonding interactions involving the para-amine group acting both as a donor and an acceptor. In the structure of the sodium salt, (II), the Na(+) cation is coordinated by five O-atom donors, one from a single monodentate arsonate ligand, two from monodentate water molecules and two from bridging water molecules, giving a very distorted square-pyramidal coordination environment. The water bridges generate one-dimensional chains extending along c and extensive interchain O-H...O and N-H...O hydrogen-bonding interactions link these chains, giving an overall three-dimensional structure. The two structures reported here are the first reported examples of salts of p-arsanilic acid.

Structural analyses of (1->3),(1->4)-β-D-glucan of oats and barley

The structures of (1→3),(1→4)-β-D-glucans of oat bran, whole-grain oats and barley and processed foods were analysed. Various methods of hydrolysis of β-glucan, the content of insoluble fibre of whole grains of oats and barley and the solution behaviour of oat and barley β-glucans were studied. The isolated soluble β-glucans of oat bran and whole-grain oats and barley were hydrolysed with lichenase, an enzyme specific for (1→3),(1→4)-β-D-β-glucans. The amounts of oligosaccharides produced from bran were analysed with capillary electrophoresis and those from whole-grains with high-performance anion-exchange chromatography with pulse-amperometric detection. The main products were 3-O-β-cellobiosyl-D-glucose and 3-O-β-cellotriosyl-D-glucose, the oligosaccharides which have a degree of polymerisation denoted by DP3 and DP4. Small differences were detected between soluble and insoluble β-glucans and also between β-glucans of oats and barley. These differences can only be seen in the DP3:DP4 ratio which was higher for barley than for oat and also higher for insoluble than for soluble β-glucan. A greater proportion of barley β-glucan remained insoluble than of oat β-glucan. The molar masses of soluble β-glucans of oats and barley were the same as were those of insoluble β-glucans of oats and barley. To analyse the effects of cooking, baking, fermentation and drying, β-glucan was isolated from porridge, bread and fermentate and also from their starting materials. More β-glucan was released after cooking and less after baking. Drying decreased the extractability for bread and fermentate but increased it for porridge. Different hydrolysis methods of β-glucan were compared. Acid hydrolysis and the modified AOAC method gave similar results. The results of hydrolysis with lichenase gave higher recoveries than the other two. The combination of lichenase hydrolysis and high-performance anion-exchange chromatography with pulse-amperometric detection was found best for the analysis of β-glucan content. The content of insoluble fibre was higher for barley than for oats and the amount of β-glucan in the insoluble fibre fraction was higher for oats than for barley. The flow properties of both water and aqueous cuoxam solutions of oat and barley β-glucans were studied. Shear thinning was stronger for the water solutions of oat β-glucan than for barley β-glucan. In aqueous cuoxam shear thinning was not observed at the same concentration as in water but only with high concentration solutions. Then the viscosity of barley β-glucan was slightly higher than that of oat β-glucan. The oscillatory measurements showed that the crossover point of the G´ and G´´ curves was much lower for barley β-glucan than for oat β-glucan indicating a higher tendency towards solid-like behaviour for barley β-glucan than for oat β-glucan.