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Up-regulation of GABA(B) receptors by chronic administration of the GABA(B) receptor antagonist SCH 50,911.

Chronic treatment of mice with the specific gamma-aminobutyric acid(B) (GABA(B)) receptor antagonist (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50,911) increased both the number of GABA(B) receptors in the whole brain (measured as [3H]CGP 54626 [S-(R,R)]-3-[[1-(3,4-dichlorophenyl)amino]-2-hydroxypropyl](cyclohexylmethyl)phosphinic acid hydrochloride binding) and the ability of baclofen to activate GABA(B) receptor coupled G-protein (measured as % reduction of the EC50 of baclofen to activate [35S]GTP(gamma)S binding). The results indicate that persistent blockade of GABA(B) receptors leads to their compensatory up-regulation and suggest that GABA(B) receptors are tonically activated by endogenous GABA.

Animals↗

In vivo blockade of thalamic GABA(B) receptors increases excitatory amino-acid levels.

The effect of intrathalamic application of GABA(B) receptor antagonists on the basal excitatory amino-acid levels was studied using microdialysis probes implanted in the dorsal lateral geniculate nucleus and in the ventrobasal complex. In both nuclei, continuous perfusion of the GABA(B) receptor antagonist 3-aminopropyl-(diethoxymethyl)-phosphinic acid (CGP 35348) produced an increase in the extracellular concentration of aspartate and (to a lesser extent) glutamate, but no change was observed in the level of taurine, the main amino acid involved in the regulation of brain osmolarity processes. In contrast, 3-amino-2-hydroxy-2-(4-chlorophenyl)-propanesulphonic acid (2-hydroxy-saclofen), another GABA(B) receptor antagonist, failed to affect the extracellular concentration of aspartate, glutamate and taurine. Thus, the basal level of excitatory amino acids in the thalamus in vivo is under the control of CGP 35348-sensitive GABA(B) receptors.

Animals↗

AMPA and GABA(B) receptor antagonists and their interaction in rats with a genetic form of absence epilepsy.

The effects of combined and single administration of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, 7,8-methylenedioxy-1-(4-aminophenyl)-4-methyl-3-acetyl-4,5-dihydro-2,3-benzodiazepine (LY 300164), and of the GABA(B) receptor antagonist gamma-aminopropyl-n-butyl-phosphinic acid (CGP 36742), on spontaneously occurring spike-wave discharges were investigated in WAG/Rij rats. LY 300164 had minor effects; only the highest dose (16 mg/kg) reduced the number of spike-wave discharges in a short time window. CGP 36742 was more effective as it significantly reduced the number of spike-wave discharges and shortened their duration at the doses of 25 and 100 mg/kg. The ED(50) values for the inhibition of spike-wave discharges by LY 300164 and CGP 36742 in a time window 30-60 min after injection were 15.5 and 16.6 mg/kg, respectively. The ED(50) of CGP 36742 was reduced to 8.0 mg/kg when this antagonist was administered in combination with LY 300164 (6 mg/kg). The interaction between the two antagonists appeared to be additive according to isobolographic analysis. Importantly, CGP 36742 and LY 300164 administered either alone or in combination had no apparent effects on behavior. These results may provide information for a rational approach to polytherapy for the treatment of generalized absence epilepsy.

Animals↗

A gadolinium(III) complex of a carboxylic-phosphorus acid derivative of diethylenetriamine covalently bound to inulin, a potential macromolecular MRI contrast agent.

A novel conjugate of a polysaccharide and a Gd(III) chelate with potential as contrast agent for magnetic resonance imaging (MRI) was synthesized. The structure of the chelate was derived from H5DTPA by replacing the central pendant arm by a phosphinic acid functional group, which was covalently bound to the polysaccharide inulin. On the average, each monosaccharide unit of the inulin was attached to approximately one (0.9) chelate moiety. The average molecular weight is 23110 and the average number of Gd3+ ions per molecule is 24. The ligand binds the Gd3+ ion in an octadentate fashion via three nitrogen atoms, four carboxylate oxygen atoms, and one P-O oxygen atom, and its first coordination sphere is completed by a water molecule. This compound shows promising properties for application as a contrast agent for MRI thanks to a favorable residence lifetime of this water molecule (170 ns at 298 K), a relatively long rotational correlation time (866 ps at 298 K), and the presence of two water molecules in the second coordination sphere of the Gd3+ ion. Furthermore, its stability toward transmetalation with Zn(II) is as high as that of the clinically used [Gd(DTPA)(H2O)]2-.

Contrast Media↗

Analysis of responses to kava kava in the feline pulmonary vascular bed.

This study was designed to test the hypothesis that kava kava induces a depressor response in the pulmonary vascular bed of the cat and to identify the pathways involved in the mediation or modulation of these effects. In separate experiments, the effects of L-N5-(1-iminoethyl)ornithine hydrochloride (L-NIO), a nitric oxide synthase inhibitor, glibenclamide, an ATP-sensitive K+ channel blocker, meclofenamate, a nonselective cyclooxygenase inhibitor, nicardipine, a calcium channel blocker, bicuculline, a gamma-aminobutyric acid (GABA)A receptor antagonist, and saclofen, a GABAB antagonist, were investigated on pulmonary arterial responses to kava kava (kava), pinacidil, an ATP-sensitive K+ channel activator, bradykinin, an inducer of nitric oxide synthase, 3-aminopropyl(methyl)phosphinic acid hydrochloride (SKF-97541), a GABAB receptor agonist, and muscimol, a GABAA receptor agonist. Lobar arterial perfusion pressure and systemic pressure were continuously monitored, electronically averaged, and recorded. Under elevated tone conditions in the isolated left lower lobe of the feline vascular bed, kava induced a dose-dependent vasodepressor response that was not significantly altered after administration of L-NIO, glibenclamide, meclofenamate, or saclofen. Responses to kava were significantly reduced after administration of either nicardipine or bicuculline. When the calcium channel blocker nicardipine was administered in addition to the GABA blocker bicuculline, there was near complete attenuation of the kava-induced vasodepressor responses. The results of this investigation suggest that kava has potent vasodepressor activity in the feline lung bed and that this response is mediated or modulated by both a calcium channel- and GABA receptor-sensitive pathway.

Animals↗

Baclofen influences lipopolysaccharide-mediated interleukin-6 release from murine pituicytes.

Pituicytes, the glial cells of the neurohypophysis, secrete interleukin-6 upon stimulation with various inflammatory mediators, i.e. lipopolysaccharide. Previous studies have identified several receptors on pituicytes. This study investigates the effect of GABA(B) receptor activation on interleukin-6 release from pituicytes. Cultured murine pituicytes were stimulated for 24 h with lipopolysaccharide (0.5 ng/ml) to give a significant interleukin-6 release compared to control. The interleukin-6 release was significantly potentiated by the GABA(B) receptor agonist (R)-4-amino-3-(4-chlorophenyl) butanoic acid (R-baclofen; 10, 100 or 500 microM). However, R-baclofen itself (10, 100 or 500 microM) did not stimulate the interleukin-6 secretion. Furthermore, the potent GABA(B) receptor antagonists 3-[[(3,4-Dichlorophenyl)methyl]amino]propyl]diethoxymethyl) phosphinic acid (CGP52432; 30 or 300 microM) and (RS)-3-Amino-2-(4-chlorophenyl)-2-hydroxypropyl-sulphonic acid (2-OH-saclofen; 10 or 100 microM) did not remove the effect of R-baclofen (100 microM). Gamma-amino butyric acid (GABA; 30 or 300 microM) did not alter the lipopolysaccharide-mediated interleukin-6 response. After 30 min, intracellular cyclic AMP (cAMP) was higher in cells stimulated with lipopolysaccharide compared to control, and R-baclofen significantly inhibited this increase in cAMP. Nevertheless, neither lipopolysaccharide nor R-baclofen had any effect on intracellular cAMP after 24 h of stimulation. The results suggest that the effect of R-baclofen on lipopolysaccharide-stimulated interleukin-6 secretion is independent of GABA(B) receptors.

Animals↗

Synthesis and characterisation of dimeric eight-coordinate lanthanide(III) complexes of a macrocyclic tribenzylphosphinate ligand.

The macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7-triyl(methylenebenzyl-phosphinic acid) H3L3, has been prepared and its complexes with Eu, Gd and Tb(III) studied by NMR, relaxometry, luminescence and single crystal X-ray crystallography. In solution and in the crystal, the complexes have eight-coordinate metal centres with bridging phosphinate groups linking the two twisted square antiprismatic coordination polyhedra. A single stereoisomer crystallises from solution with an RRR and SSS configuration at the P centres in each sub-unit. The relaxivity of [GdL3]2 is low (1.9 mM-1 s-1, 298 K, 20 MHz), consistent with the absence of any proximate water molecules. The terbium dimer possesses a relatively long excited state lifetime (2.47 ms, 298 K).

Journal Article↗

D-alanine: D-alanine ligase of Escherichia coli. Expression, purification and inhibitory studies on the cloned enzyme.

A 1.2 kb BamHI fragment from pDK30 [Robinson, Kenan, Sweeney & Donachie (1986) J. Bacteriol. 167, 809-817] was cloned in pDOC55 [O'Connor & Timmis (1987) J. Bacteriol. 169, 4457-4482] to give two constructs, pDOC89 and pDOC87, in which the Escherichia coli D-alanine:D-alanine ligase (EC 6.3.2.4) gene (ddl) was placed under the control of the lac and lambda PL promoters respectively. Both constructs, when used to transform E. coli M72, gave similar levels of expression of the ddl gene. The expressed enzyme was purified to homogeneity and the amino acid sequence of its N-terminal region was found to be consistent with that predicted from the gene sequence, except that the N-terminal methionine was not present in the mature protein. [1(S)-Aminoethyl][(2RS)2-carboxy-1-octyl]phosphinic acid (I), previously shown to bind tightly to Enterococcus faecalis and Salmonella typhimurium D-alanine:D-alanine ligases following phosphorylation Parsons, Patchett, Bull, Schoen, Taub, Davidson, Combs, Springer, Gadebusch, Weissberger, Valiant, Mellin & Busch (1988) J. Med. Chem. 31, 1772-1778; Duncan & Walsh (1988) Biochemistry 27, 3709-3714], was found to be a classical slow-binding inhibitor of the E. coli ligase.

Amino Acid Sequence↗

Structure and magnetism of a new hydrogen-bonded layered cobalt(II) network, constructed by the unprecedented carboxylate-phosphinate ligand [O2(C6H5)PCH2CO2]2-.

By hydrothermal reaction of CoCl2 x 6H2O with K2pcc (H2pcc = phenyl(carboxymethyl) phosphinic acid) at 423 K, a novel hybrid material of formula [Co2(pcc)2 (H2O)2] x H2O has been obtained. The compound, which is the first pcc/metal complex reported, exhibits a polymeric arrangement, where cobalt metal ions, linked together by bridging carboxylate and phosphinate oxygens, form infinite chains of edge-shared CoO6 octahedra. The cobalt chains are in turn linked together through important hydrogen-bonding interactions, which create an infinite 2D architecture. The two crystallographically independent cobalt centers, both displaying distorted octahedral coordination, present different environments as one is surrounded by six ligand oxygens and the other by four ligand oxygens and by two water oxygens. Careful magnetic studies performed by a home-built alternating current susceptometer reveal that the system undergoes an antiferromagnetic transition below 2.0 K leading to a canted structure. Field-dependent studies further indicate the occurrence of a metamagnetic transition at a critical field of 650 +/- 50 G.

Journal Article↗

Palladium-catalyzed hydrophosphinylation of alkenes and alkynes.

Various palladium catalysts promote the addition of hypophosphorous derivatives ROP(O)H(2) to alkenes and alkynes in good yields and under mild conditions. Particularly, Cl(2)Pd(PPh(3))(2)/2 MeLi, and Pd(2)dba(3)/xantphos allow for phosphorus-carbon bond formation instead of transfer hydrogenation. Commercial aqueous solutions of hypophosphorous acid can be employed successfully at ambient temperature. With styrene and terminal alkynes, the regioselectivity (linear versus branched products) can be controlled to some extent with the catalytic system employed. The methodology considerably extends upon previous routes for the preparation of H-phosphinic acids and other organophosphorus compounds.

Journal Article↗

Synthesis and enzymic evaluation of 4-mercapto-6-oxo-1, 4-azaphosphinane-2-carboxylic acid 4-oxide as an inhibitor of mammalian dihydroorotase.

The design, synthesis, and enzymic evaluation of cis- and trans-4-mercapto-6-oxo-1,4-azaphosphinane-2-carboxylic acid 4-oxide 5 against mammalian dihydroorotase is presented. The design strategy for 5 was based on the strong affinity of phosphinothioic acids for zinc and that 5 also resembles the postulated tetrahedral transition state for the enzyme-catalyzed reaction. The synthesis of 5 utilized a novel protection/deprotection sequence upon 4-hydroxy-6-oxo-1, 4-azaphosphinane-2-carboxylic acid 4-oxide 4, followed by incorporation of alpha-phenyl benzenemethanethiol and exhaustive deprotection to afford 5 in 40% overall yield from 4. The activities of both isomers of 5 as inhibitors of mammalian dihydroorotase were marginally greater than that of the parent phosphinic acid 4, indicating a weak binding enhancement due to the phosphinothioic acid moiety.

Animals↗

Synthesis and anti-herpes simplex activity of analogues of phosphonoacetic acid.

The synthesis of monoesters (P and C) of phosphonoacetic acid (PA) is given. The carboxyl esters were prepared by two methods: the reaction of chloroacetates with tris(trimethylsilyl) phosphite, followed by hydrolysis; and by the acid-catalyzed esterification of PA with the appropriate alcohol. P-Monoesters of PA were prepared either by the reaction of alkyl[bis(trimethylsilyl)] phosphite with benzyl chloroacetate followed by deprotection or by the reaction of dimethylphenyl phosphite with benzyl bromoacetate followed by hydrogenolysis. Three aryl- (alkyl-)phosphinic acid derivatives are reported. The above compounds were evaluated for anti-herpes activity against HSV-induced DNA polymerase and in animals infected with herpes dermatitis.

Acetates↗

Both GABAA and GABAB receptors participate in suppression of [CA2+]i pulsing in toad melanotrophs.

The receptor mechanisms involved in the inhibitory effect of gamma-aminobutyric acid (GABA) in suppressing spontaneous [Ca2+]i pulsing in melanotrophs of Xenopus laevis were investigated. The selective GABAB receptor agonist, baclofen reversibly arrested [Ca2+]i pulsing. This inhibition was unaffected by the selective GABAA receptor antagonist, bicuculline methiodide, but was blocked by the selective GABAB receptor antagonist, CGP 35348 (3-aminopropyl diethyoxymethyl phosphinic acid). The selective GABAA receptor agonist, muscimol, also arrested [Ca2+]i pulsing after causing a transient rise in [Ca2+]i. This biphasic response to muscimol was unaffected by CGP 35348, but was blocked by bicuculline. The inhibitory effect of GABA was unaffected by either CGP 35348 or bicuculline when given alone, but was blocked by both antagonists given together. In cells pretreated with pertussis toxin, the response to baclofen was completely lost, whereas responses to GABA and muscimol persisted; the response to GABA was blocked by bicuculline alone. Thus, both GABAA and GABAB receptors are involved in the inhibitory effect of GABA in suppressing spontaneous [Ca2+]i pulsing in Xenopus melanotrophs.

Animals↗

Differing actions of nitropropane analogs of GABA and baclofen in central and peripheral preparations.

In the guinea-pig isolated ileum, both baclofen (5-100 microM) and gamma-aminobutyric acid (GABA; 5-100 microM) induced a bicuculline-insensitive depression of cholinergic twitch contractions which was reversibly and competitively antagonised by 3-amino-1-nitropropane (50-250 microM). 3-Amino-1-nitropropane (pA2 = 5.0 +/- 0.1) was twice as potent as 2-hydroxysaclofen (pA2 = 4.5 +/- 0.1), but was equipotent with 3-aminopropyl(P-diethoxymethyl)phosphinic acid (CGP 35348) (pA2 = 4.9 +/- 0.2), and did not show any partial agonist activity at these peripheral GABAA or GABAB receptor sites. In rat neocortical slices, 3-amino-1-nitropropane did not activate GABAB receptor sites or affect baclofen-induced suppression of spontaneous discharges. In the cat spinal cord, however, under in vivo conditions, the corresponding nitro analog of baclofen 3-amino-2-(4-chloro)-nitropropane was an agonist at GABAB receptor sites, although more than 60 times weaker than baclofen in depressing monosynaptic excitatory field potentials, whereas 3-amino-1-nitropropane was an extremely weak agonist at bicuculline-sensitive GABAA sites. The differing actions of 3-amino-1-nitropropane at peripheral and central GABAB receptor sites suggest heterogeneity among these receptors.

Animals↗

Comparison of covalency in the complexes of trivalent actinide and lanthanide cations.

The complexes of trivalent actinide (Am(III) and Cm(III)) and lanthanide (Nd(III) and Sm(III)) cations with bis(2,4,4-trimethylpentyl)phosphinic acid, bis(2,4,4-trimethylpentyl)monothiophosphinic acid, and bis(2,4,4-trimethylpentyl)dithiophosphinic acid in n-dodecane have been studied by visible absorption spectroscopy and X-ray absorption fine structure (XAFS) measurements in order to understand the chemical interactions responsible for the great selectivity the dithiophosphinate ligand exhibits for trivalent actinide cations in liquid-liquid extraction. Under the conditions studied, each type of ligand displays a different coordination mode with trivalent f-element cations. The phosphinate ligand coordinates as hydrogen-bonded dimers, forming M(HL2)3. Both the oxygen and the sulfur donor of the monothiophosphinate ligand can bind the cations, affording both bidentate and monodentate ligands. The dithiophosphinate ligand forms neutral bidentate complexes, ML3, with no discernible nitrate or water molecules in the inner coordination sphere. Comparison of the Cm(III), Nd(III), and Sm(III) XAFS shows that the structure and metal-donor atom bond distances are indistinguishable within experimental error for similarly sized trivalent lanthanide and actinide cations, despite the selectivity of bis(2,4,4-trimethylpentyl)dithiophosphinic acid for trivalent actinide cations over trivalent lanthanide cations.

Journal Article↗

Pharmacologically distinct GABAB receptors that mediate inhibition of GABA and glutamate release in human neocortex.

1. The release of endogenous gamma-aminobutyric acid (GABA) and glutamic acid in the human brain has been investigated in synaptosomal preparations from fresh neocortical samples obtained from patients undergoing neurosurgery to reach deeply located tumours. 2. The basal outflows of GABA and glutamate from superfused synaptosomes were largely increased during depolarization with 15 mM KCl. The K(+)-evoked overflows of both amino acids were almost totally dependent on the presence of Ca(2+) in the superfusion medium. 3. The GABAB receptor agonist (-)-baclofen (1, 3 or 10 microM) inhibited the overflows of GABA and glutamate in a concentration-dependent manner. The inhibition caused by 10 microM of the agonist ranged from 45-50%. 5. The effect of three selective GABAB receptor antagonists on the inhibition of the K(+)-evoked GABA and glutamate overflows elicited by 10 microM (-)-baclofen was investigated. Phaclofen antagonized (by about 50% at 100 microM; almost totally at 300 microM) the effect of (-)-baclofen on GABA overflow but did not modify the inhibition of glutamate release. The effect of (-)-baclofen on the K(+)-evoked GABA overflow was unaffected by 3-amino-propyl (diethoxymethyl)phosphinic acid (CGP 35348; 10 or 100 microM); however, CGP 35348 (10 or 100 microM) antagonized (-)-baclofen (complete blockade at 100 microM) at the heteroreceptors on glutamatergic terminals. Finally, [3-[[(3,4-dichlorophenyl) methyl]amino]propyl] (diethoxymethyl) phosphinic aid (CGP 52432), 1 microM, blocked the GABAB autoreceptor, but was ineffective at the heteroreceptors. The selectivity of CGP 52423 was lost at 30 microM, as the compound, at this concentration, inhibited completely the (-)-baclofen effect on both GABA and glutamate release. 5. It is concluded that GABA and glutamate release evoked by depolarization of human neocortex nerve terminals can be affected differentially through pharmacologically distinct GABAB receptors.

Aged↗

The effects of intraperitoneal and intracerebroventricular administration of the GABAB receptor antagonist CGP 35348 on food intake in rats.

In order to test the hypothesis that endogenous gamma-aminobutyric acid (GABA), acting at central GABAB receptors, plays a physiological role in the control of feeding behaviour, it was reasoned that blocking these receptors with a centrally active GABAB receptor antagonist should reduce food intake in hungry rats. In the present study, experiments were carried out to test this possibility using the GABAB receptor antagonist 3-aminopropyl-diethoxy-methyl-phosphinic acid (CGP 35348), which is water-soluble and can penetrate the blood-brain barrier from the systemic circulation. CGP 35348 (50 and 100 mg/kg, i.p.) had no effect on food intake in 22-h fasted rats, but a higher dose (i.e. 500 mg/kg., i.p.) significantly reduced cumulative food consumption. These findings are consistent with previous observations that high systemic doses of CGP 35348 are needed to block central GABAB receptors. However, to eliminate the possibility that the 500 mg/kg dose of CGP 35348 decreased food intake by a peripheral, rather than a central mode of action, further experiments were undertaken where the drug was given directly into the brain by the intracerebroventricular (i.c.v.) route. I.c.v. administration of CGP 35348 (5 and 10 microg) significantly decreased cumulative food intake food intake in rats that had been fasted for 22 h. By contrast, i.c.v. administration of CGP 35348 (10 microg) had no effect on water intake in 16-h water-deprived rats. The results indicate that CGP 35348 reduces food consumption in hungry rats by blocking central GABAB receptors in a behaviourally specific manner. These findings suggest that endogenous GABA acting at central GABAB receptors plays a physiological role in the regulation of feeding behaviour.

Animals↗

Importance of the gamma-aminobutyric acid(B) receptor C-termini for G-protein coupling.

Functional gamma-aminobutyric acid(B) (GABA(B)) receptors assemble from two subunits, GABA(B(1)) and GABA(B(2).) This heteromerization, which involves a C-terminal coiled-coil interaction, ensures efficient surface trafficking and agonist-dependent G-protein activation. In the present study, we took a closer look at the implications of the intracellular C termini of GABA(B(1)) and GABA(B(2)) for G-protein coupling. We generated a series of C-terminal mutants of GABA(B(1)) and GABA(B(2)) and tested them for physical interaction, surface trafficking, coupling to adenylyl cyclase, and G-protein-gated inwardly rectifying potassium channels in human embryonic kidney (HEK) 293 cells as well as on endogenous calcium channels in sympathetic neurons of the superior cervical ganglion (SCG). We found that the C-terminal interaction contributes only partly to the heterodimeric assembly of the subunits, indicating the presence of an additional interaction site. The described endoplasmic reticulum retention signal within the C terminus of GABA(B(1)) functioned only in the context of specific amino acids, which constitute part of the GABA(B(1)) coiled-coil sequence. This finding may provide a link between the retention signal and its shielding by the coiled coil of GABA(B(2).) In HEK293 cells, we observed that the two well-known GABA(B) receptor antagonists [S-(R*,R*)]-[3-[[1-(3,4-dichlorophenyl)ethyl]amino]-2-hydroxypropyl](cyclohexylmethyl) phosphinic acid (CGP54626) and (+)-(2S)-5,5-dimethyl-2-morpholineacetic acid (SCH50911) CGP54626 and SCH50911 function as inverse agonists. The C termini of GABA(B(1)) and GABA(B(2)) strongly influenced agonist-independent G-protein coupling, although they were not necessary for agonist-dependent G-protein coupling. The C-terminal GABA(B) receptor mutants described here demonstrate that the active receptor conformation is stabilized by the coiled-coil interaction. Thus, the C-terminal conformation of the GABA(B) receptor may determine its constitutive activity, which could be a therapeutic target for inverse agonists.

Adenylyl Cyclases↗