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J A Peters

Publications and source records attributed to J A Peters.

At least 73 records · Page 4Linked to original sources
PubMed1995

Selective alkaline oxidative degradation of mono- and di-saccharides by hydrogen peroxide using borate as catalyst and protecting group.

Lactose, maltose, cellobiose, and galactose can be degraded selectively in one step and in high yield into the corresponding next lower aldose and formic acid by H2O2 in the presence of borate. The selectivity further improves when a small amount of EDTA is added, in order to suppress the influence of transition metal ions which catalyze the decomposition of H2O2 via radical pathways, leading to non-selective oxidative degradation of aldoses. The function of borate in the selective oxidative degradation of aldoses is two-fold: catalysis of the degradation of the starting aldose and protection of the next lower aldose against oxidation.

Borates↗
PubMed1995

Neurosteroids and GABAA receptor function.

In 1984, a potent and selective interaction of the steroidal anaesthetic alphaxalone with the GABAA receptor was demonstrated. Subsequent studies established that certain naturally occurring steroids were potent positive allosteric modulators of the GABAA receptor. Although peripheral endocrine glands are an important endogenous source, the brain can synthesize 'neurosteroids', and these have the potential to influence the activity of the GABAA receptor in the CNS. Systemic administration of steroids have clear behavioural effects. In this article, Jeremy Lambert and colleagues review recent advances in this field and discuss the therapeutic potential of this novel, non-genomic effect of steroids and investigate whether they may influence behaviour under physiological, or pathophysiological, conditions.

Anesthetics↗
PubMed1995

An electrophysiological investigation of the properties of a murine recombinant 5-HT3 receptor stably expressed in HEK 293 cells.

1. The pharmacological and biophysical properties of a recombinant 5-HT3 receptor have been studied by use of patch-clamp techniques applied to HEK 293 cells stably transfected with the murine 5-HT3 R-A cDNA. 2. At a holding potential of -60 mV, 77% of cells investigated responded to ionophoretically applied 5-HT with an inward current. Such currents were unaffected by methysergide (1 microM), or ketanserin (1 microM), but were antagonized in a concentration-dependent and reversible manner by the selective 5-HT3 receptor antagonist, ondansetron (IC50 = 440 pM) and the non-selective antagonists (+)-tubocurarine (IC50 = 1.8 nM) and metoclopramide (IC50 50 nM). 3. The 5-HT-induced current reversed in sign (E5-HT) at approximately -2mV and exhibited inward rectification. The influence of extra- and intracellular ion substitutions upon E5-HT indicates the 5-HT-evoked current to be mainly mediated by a mixed monovalent cation conductance. 4. Calcium and magnesium (0.1-10 nM) produced a concentration-dependent, voltage-independent, inhibition of the 5-HT-induced response. Zinc (0.3-300 microM) exerted a biphasic effect with low concentrations enhancing, and high concentrations depressing, the 5-HT-evoked current. 5. Fluctuation analysis of inward currents evoked by a low (1 microM) concentration of 5-HT suggests the current to be mediated by the opening of channels with a conductance of 420 fS. 6. The pharmacological and biophysical properties of the 5-HT3 R-A are similar to those previously described for 5-HT3 receptors native to murine neuroblastoma cell lines, with the exception that the function of the recombinant receptor was enhanced by low concentrations of zinc. This observation suggests that the properties of the native receptor are not completely represented by the 5-HT3 R-A subunit alone.

Animals↗
PubMed1995

The interaction of trichloroethanol with murine recombinant 5-HT3 receptors.

1. The effects of ethanol, chloral hydrate and trichloroethanol upon the 5-HT3 receptor have been investigated by use of electrophysiological techniques applied to recombinant 5-HT3 receptor subunits (5-HT3R-A or 5-HT3R-As) expressed in Xenopus laevis oocytes. Additionally, the influence of trichloroethanol upon the specific binding of [3H]-granisetron to membrane preparations of HEK 293 cells stably transfected with the murine 5-HT3R-As subunit and 5-HT3 receptors endogenous to NG 108-15 cell membranes was assessed. 2. Ethanol (30-300 mM), chloral hydrate (1-30 mM) and trichloroethanol (0.3-10 mM), produced a reversible, concentration-dependent, enhancement of 5-HT-mediated currents recorded from oocytes expressing either the 5-HT3R-A, or the 5-HT3R-As subunit. 3. Trichloroethanol (5 mM) produced a parallel leftward shift of the 5-HT concentration-response curve, reducing the EC50 for 5-HT from 1 +/- 0.04 microM (n = 4) to 0.5 +/- 0.01 microM (n = 4) for oocytes expressing the 5-HT3R-A. A similar shift, from 2.1 +/- 0.05 microM (n = 11) to 1.3 +/- 0.1 microM (n = 4), was observed in oocytes expressing the 5-HT3R-As subunit. Trichloroethanol (5 mM) had little or no effect upon the maximum current produced by 5-HT for either recombinant receptor. 4. Trichloroethanol (5 mM) similarly reduced the EC50 for 2-methyl-5-HT from 13 +/- 0.4 microM (n = 4) to 4.6 +/- 0.2 microM (n = 4) and from 15 +/- 2 microM (n = 4) to 5 +/- 0.4 microM (n = 4) for oocytes expressing the 5-HT3R-A and 5-HT3R-As subunit respectively. Additionally, trichloroethanol (5 mM) produced a clear enhancement of the maximal current to 2-methyl-5-HT (expressed as a percentage of the maximal current to 5-HT) from 63 +/- 0.7% (n = 4) to 101 +/- 1.6% (n = 4) and from 9 +/- 0.2% (n = 4) to 74 +/- 2% (n = 4) for oocytes expressing the 5-HT3R-A and 5-HT3R-As subunit respectively. 5. Trichloroethanol (2.5 mM) had no effect upon the Kd, or Bmax, of specific [3H]-granisetron binding to membrane homogenates of NG 108-15 cells or HEK 293 cells. Similarly, competition for [3H]-granisetron binding by the 5-HT3 receptor antagonists ondansetron and tropisetron was unaffected. However, competition for [3H]-granisetron binding by the 5-HT3 receptor agonists, 5-HT, 2-methyl-5-HT and phenylbiguanide was enhanced by trichloroethanol (2.5 mM). 6 Unexpectedly, the competition for [3H]-granisetron binding by the 5-HT3 receptor antagonist,quipazine, was enhanced by 2.5 mM trichloroethanol. Quipazine (1 nM-0.3 microM) antagonized 5-HT evoked currents recorded from oocytes expressing the 5-HT3R-A subunit with an IC50 of 18 +/- 3 nM(n = 4). Additionally, quipazine (30 nM-0.3 microM) produced a small inward current which was greatly enhanced by 5 mM trichloroethanol and antagonized by 100 nM ondansetron. Collectively, these observations suggest that quipazine may act as a partial agonist.7. The demonstration that a recombinant homo-oligomeric receptor, expressed in a foreign membrane,retains a sensitivity to alcohols, together with the sequencing of alcohol-insensitive 5-HT3 receptor subunits, may lead to a better definition of the alcohol binding site(s).

Animals↗
PubMed1995

Evidence that the atypical 5-HT3 receptor ligand, [3H]-BRL46470, labels additional 5-HT3 binding sites compared to [3H]-granisetron.

1. The radioligand binding characteristics of the 3H-derivative of the novel 5-HT3 receptor antagonist BRL46470 were investigated and directly compared to the well characterized 5-HT3 receptor radioligand [3H]-granisetron, in tissue homogenates prepared from rat cerebral cortex/hippocampus, rat ileum, NG108-15 cells, HEK-5-HT3As cells and human putamen. 2. In rat cerebral cortex/hippocampus, rat ileum, NG108-15 cell and HEK-5-HT3As cell homogenates, [3H]-BRL46470 bound with high affinity (Kd (nM): 1.57 +/- 0.18, 2.49 +/- 0.30, 1.84 +/- 0.27, 3.46 +/- 0.36, respectively; mean +/- s.e. mean, n = 3-4) to an apparently homogeneous saturable population of sites (Bmax (fmol mg-1 protein): 102 +/- 16, 44 +/- 4, 968 +/- 32 and 2055 +/- 105, respectively; mean +/- s.e. mean, n = 3-4) but failed to display specific binding in human putamen homogenates. 3. In the same homogenates of rat cerebral cortex/hippocampus, rat ileum, NG108-15 cells, HEK-5-HT3As cells and human putamen as used for the [3H]-BRL46470 studies, [3H]-granisetron also bound with high affinity (Kd (nM): 1.55 +/- 0.61, 2.31 +/- 0.44, 1.89 +/- 0.36, 2.03 +/- 0.42 and 6.46 +/- 2.58 respectively; mean +/- s.e. mean, n = 3-4) to an apparently homogeneous saturable population of sites (Bmax (fmol mg-1 protein): 39 +/- 4, 20 +/- 2, 521 +/- 47, 870 +/- 69 and 18 +/- 2, respectively; mean +/- s.e. mean, n = 3-4). 4. Competition studies with a range of structurally different 5-HT3 receptor ligands indicated that in both rat cerebral cortex/hippocampus and rat ileum homogenates, [3H]-BRL46470 binding exhibited a pharmacological profile consistent with the labelling the 5-HT3 receptor with compounds competing with Hill coefficients close to unity.5 In HEK-5-HT3As cell homogenates, [3H]-BRL46470 and [3H]-granisetron associated rapidly((3.84+/-0.4)106 M-1S-1 and (5.85+/-0.2)106 M-1S-1, respectively, mean+/-s.e.mean, n=3-4) in an apparently monophasic manner. Following the establishment of equilibrium, both [3H]-BRL46470 and [3H]-granisetron at a saturating concentration ([3H]-BRL46470 approximately 16 nM; [3H]-granisetron approximately 18 nM) and at a sub-Kd concentration (approximately 1 nm for both radioligands)dissociated biphasically in HEK-5-HT3As cell homogenates (saturating concentration; [3H]-BRL464704.05 x 10-3+/-2.53 x I0-3 s-1 and 5.83 x 10-5+0.91 x I0-5 s-1; [3H]-granisetron 3.20 x 10-3+ 1.70 x IO-3 s-1 and18.58 x 10-5 +/- 4.19 x I0-5 s-1: sub-Kd concentration; [3H]-BRL46470 2.47 x 10-3+/- 1.18 x 10-3 s-1 and 9.30x 10-5+/-2.59x 10-5 S-1; [3H]-granisetron 65.91 x 10-3+/-22.14x I0-3 s-1 and 49.96x 10-5+/-12.26x 10-5s- 1 mean+/- s.e.mean, n = 4-8) when induced by a 300 fold dilution in ice-cold Tris/Krebs.6 In conclusion, the present study provides evidence that [3H]-BRL46470 specifically labels the 5-HT3receptor in rat cerebral cortex/hippocampus, rat ileum, NG108-15 cell and HEK-5-HT3As cell homogenates, but fails to label the 5-HT3 receptor expressed in human putamen. Whilst the pharmacological profile of the site labelled by [3H]-BRL46470 is directly comparable to that labelled by [3H]-granisetron, [3H]-BRL46470 consistently labelled approximately twice the density of sites compared to [3H]-granisetron in the same tissue homogenates prepared from rat cortex/hippocampus, ratileum, NG108-15 cells and HEK-5-HT3As cells.

Animals↗
PubMed1995

Cloning and functional expression of a human 5-hydroxytryptamine type 3AS receptor subunit.

A human 5-hydroxytryptamine receptor type 3AS (5-HT3R-AS) subunit has been cloned from an amygdala cDNA library. We report the nucleotide and predicted amino acid sequence of the human subunit, which possesses 85% and 84% amino acid sequence identity with mouse and rat 5-HT3R-AS subunits, respectively. Acting on Xenopus laevis oocytes injected with RNA transcripts of the clone, 5-HT and selective 5-HT3 receptor agonists elicited inwardly directed current responses that displayed desensitization. Such currents were blocked in a concentration-dependent manner by selective and nonselective 5-HT3 receptor antagonists but were unaffected by compounds acting at G protein-linked 5-HT receptors. A quantitative comparison of the pharmacological profiles of human and mouse recombinant 5-HT3R-AS receptor complexes revealed differences in the potencies of some antagonist or agonist compounds tested, the most dramatic example being (+)-tubocurarine, which demonstrated an approximately 1800-fold discrepancy in antagonist potency. In view of the small number of sequence substitutions that occur between the human and mouse homologues of the 5-HT3R-AS in the extracellularly located aminoterminal domain, compounds such as (+)-tubocurarine, in conjunction with site-directed mutagenesis, may prove to be valuable in locating amino acid residues that contribute to the ligand binding site(s) of the 5-HT3 receptor. Also, when methodological differences are taken into account, the present study suggests that a homo-oligomeric assembly of human 5-HT3R-AS subunits can account for the distinctive ligand binding properties of human 5-HT3 receptors established in postmortem brain tissue.

Amino Acid Sequence↗
PubMed1994

Cloning and functional expression of a Drosophila gamma-aminobutyric acid receptor.

A cDNA encoding a functional gamma-aminobutyric (GABA)-activated Cl- channel has been isolated from an adult Drosophila head cDNA library. When expressed in Xenopus laevis oocytes, the subunit functions efficiently, presumably as a homooligomeric complex and is activated by GABA or muscimol. GABA-evoked currents are highly sensitive to antagonism by picrotoxin but are insensitive to bicuculline, RU 5135, or zinc. Pentobarbitone greatly enhances GABA-evoked currents, whereas the neurosteroid 5 alpha-pregnan-3 alpha-ol-20-one demonstrates a large reduction in both the potency and maximal effect when compared with its actions upon vertebrate GABA type A receptors. Although zinc-insensitive, the subunit is also insensitive to flunitrazepam. Hence, the GABA receptors formed by this subunit exhibit a unique pharmacology when compared with vertebrate GABA type A receptors or those composed of rho subunits. Because the receptor-channel complex functions as a homooligomer, this subunit may be of value in mutagenesis studies aiming to define drug-binding sites.

Amino Acid Sequence↗
PubMed1994

The structure and (local) stability constants of borate esters of mono- and di-saccharides as studied by 11B and 13C NMR spectroscopy.

The formation of borate esters of various mono- and di-saccharides in aqueous solution was studied by 11B and 13C NMR spectroscopy. Association constants K(B-L) at a carbohydrate-borate molar ratio of 1:1, pH 7, and 25 degrees C were determined and compared with literature values obtained from potentiometry. The association constants K(B-L) were converted into local association constants Kloc(B-L) by using the distribution of the various anomeric forms in D2O. In this way, values of Kloc(B-L) were obtained, which appear to be characteristic of the configuration concerned. They explain the favourable effect of borate in the alkaline isomerisation of lactose into lactulose. At a low molar ratio (1:3) of carbohydrate-borate, predominantly diborate esters (B-)2L were formed.

Borates↗
PubMed1994

Influence of sex-steroid hormones on the regulation of lymphocyte beta 2-adrenoceptors during the menstrual cycle.

1. Up to 40% of female asthmatic subjects suffer a premenstrual deterioration in their condition which may be ameliorated by progesterone supplementation, although the mechanism responsible for this phenomenon is not understood. In vitro studies have shown that female sex-steroid hormones potentiate the bronchorelaxant effect of isoprenaline, whilst in vivo it has been shown that females exhibit greater sensitivity of systemic beta 2-adrenoceptor responses. 2. The aim of the present study was to determine whether cyclical alterations in beta 2-adrenoceptor expression, occurring under the influence of ovarian sex-steroid hormones, may offer an explanation for these findings. In vitro parameters of lymphocyte beta 2-adrenoceptor function were investigated in nine normal female subjects (aged 24 +/- 2 years) during the follicular (day 2-4) and luteal (day 21-23) phases of their menstrual cycle, and results were compared with those of nine age-matched healthy male controls studied at the same time intervals. 3. In female subjects there were significant increases in serum concentrations of oestradiol (3.3-fold) and progesterone (10.6-fold) between the follicular and luteal phases of the menstrual cycle, whereas no changes occurred in males. 4. In females during the luteal phase, the increase in sex-steroid hormones was mirrored by an increase in lymphocyte beta 2-adrenoceptor density (Bmax) and in maximal cyclic AMP response to isoprenaline (Emax), which were significantly higher than in male subjects. Mean differences (95% CI) between male and female subjects on visit 2 were 1.09 (0.49 to 1.69) fmol/10(6) cells (P = 0.001) for Bmax, and 3.42 (0.80 to 6.04) pmol/10(6) cells (P = 0.02) for Emax.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Cloning and functional expression of an apparent splice variant of the murine 5-HT3 receptor A subunit.

The polymerase chain reaction has been employed to isolate a cDNA encoding a functional 5-HT3 receptor subunit from the murine neuroblastoma cell line N1E-115. Overall, the amino acid sequence predicted from this clone demonstrates a 98% homology with the 5-HT3 receptor A subunit cloned from NCB-20 hybridoma cells. A deletion of 6 amino acid residues located within the putative large intracellular loop, which may result from alternative splicing, represents the principal difference between the two clones. Upon expression in Xenopus oocytes, the homo-oligomeric receptor displayed pharmacological properties which define it as a functional 5-HT3 receptor.

Amino Acid Sequence↗
PubMed1993

An electrophysiological investigation of the properties of 5-HT3 receptors of rabbit nodose ganglion neurones in culture.

1. The biophysical and pharmacological properties of 5-hydroxytryptamine (5-HT)-evoked currents in rabbit nodose ganglion neurones in culture have been determined by use of the whole-cell and outside-out membrane patch recording modes of the patch-clamp technique. 2. In 49% of cells investigated the bath application of 10(-5) M 5-HT at negative holding potentials elicited an inward current. The whole-cell response to 5-HT reversed in sign (E5-HT) at approximately -2 mV and exhibited inward rectification. 3. The influence of various ion substitutions upon E5-HT established that the 5-HT-evoked current is mainly mediated by a mixed Na+, K+ cation conductance with little or no contribution from Cl- ions. The omission of Ca2+ and Mg2+ from the extracellular solution enhanced the amplitude of the 5-HT-induced current. 4. On isolated outside-out membrane patches, the bath application of 10(-6) M 5-HT induced single channel currents with a chord conductance of approximately 17 pS at -70 mV and an average slope conductance of 19 pS over the range -100 to -40 mV. The 5-HT-induced single channels exhibited modest inward rectification and were reduced in frequency, but not amplitude, by the 5-HT3 receptor antagonist metoclopramide (10(-6) M). 5. The bath application of 5-HT (3 x 10(-7)-3 x 10(-5) M) to whole cells voltage clamped at -60 mV produced dose-dependent inward currents which were mimicked by 2-methyl-5-HT and 1-phenylbiguanide with equipotent molar ratios, relative to 5-HT, of 2.5 and 32 respectively. 6. Whole-cell inward currents produced by the local pressure application of 5-HT (10(-5) M) were unaffected by 10(-6) M methysergide, 10(-6) M ketanserin or 10(-6) M citalopram, but were concentration-dependently antagonized by the selective 5-HT3 receptor antagonists tropisetron (IC50 = 4.6 x 10(-11) M) ondansetron (IC50 = 5.7 x 10(-11) M), and bemesetron (IC50 = 3.3 x 10(-10) M). The response to 5-HT was also blocked by the non-selective antagonists metoclopramide (IC50 = 1.2 x 10(-8) M), cocaine (IC50 = 8.3 x 10(-8) M) and (+)-tubocurarine (IC50 = 1.6 x 10(-7) M).

Animals↗
PubMed1992

Recent advances in the electrophysiological characterization of 5-HT3 receptors.

5-HT3 receptors are ligand-gated, cation-selective ion channels, mediating membrane depolarization and neuronal excitation. Established and potential therapeutic applications of selective 5-HT3 receptor antagonists, coupled with the localization of this receptor subtype within discrete areas of the CNS, have resulted in an intensification of research in this area. In this review, Jeremy Lambert and colleagues summarize recent developments in the electrophysiological characterization of 5-HT3 receptors, and comment upon the unresolved issue of 5-HT3 receptor heterogeneity.

Animals↗
PubMed1992

A patch clamp study of the nicotinic acetylcholine receptor of bovine adrenomedullary chromaffin cells in culture.

1. Acetylcholine-induced currents recorded from bovine adrenal medullary chromaffin cells maintained in culture were studied during pressure or ionophoretic applications of ACh, using the 'whole-cell' and 'outside-out' configurations of the patch clamp technique. In standard salines, ACh evoked whole-cell currents of -38 pA to -1 nA at -60 mV, which had a reversal potential (EACh) of -7.1 +/- 0.6 mV. The ACh current-voltage relationship was characteristically linear at negative holding potentials and biphasic at positive holding potentials, displaying a region of almost zero slope conductance between 0 and +40 mV followed by a region of positive slope conductance at more positive potentials. 2. Relative permeation to cations was examined. Substitution of external Na+ by sucrose resulted in a -42 mV shift of EACh for a 10-fold reduction in [Na+]o. Using isotonic substitutions, the permeability ratios (relative to Na+) for monovalent cations were determined to be 1.32 +/- 0.02 for Cs+ (n = 11), 1.03 +/- 0.02 for Li+ (n = 8) and 0.18 +/- 0.02 for Tris+ (n = 7). Elevated external Ca2+ salines were found to shift EACh to more positive potentials, especially in the presence of low external Na+. 3. The nicotinic agonists nicotine, tetramethylammonium and lobeline evoked inward currents in bovine chromaffin cells. In contrast, decamethonium and the muscarinic agonist, methacholine, had no effect. 4. The nicotinic antagonists mecamylamine, trimetaphan, (+)-tubocurarine and hexamethonium caused dose-dependent reductions in the amplitude of ACh-evoked inward currents. The estimated IC50's were 0.25, 0.33, 0.63 and 2.2 microM respectively, for cells voltage clamped at -60 mV. High concentrations (> 2 microM) of the muscarinic antagonist, atropine, also produced a dose-dependent reduction in the amplitude of ACh-induced currents. 5. Inhibition by trimetaphan was voltage independent. With the other drugs the antagonism was voltage sensitive, increasing with membrane hyperpolarization. The voltage sensitivity was most marked for hexamethonium. Neither hexamethonium nor mecamylamine were found to depress ACh-evoked outward currents at concentrations which severely depressed inward currents. In addition to its antagonist actions, (+)-tubocurarine activated unitary currents in these cells and on isolated membrane patches. 6. The results indicate that nicotinic ion channels of bovine chromaffin cells have a similar ionic selectivity to monovalent cations, but that Ca2+ ions permeate the channels to a greater degree than at the motor endplate. The ACh current-voltage relationship resembles that described for other types of 'neuronal' nicotinic receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1991

Physiological and pharmacological properties of 5-HT3 receptors--a patch clamp-study.

Whole cell and patch clamp techniques were used to investigate the properties of 5-HT3 receptors of a murine neuroblastoma cell line (N1E-115) and adult rabbit nodose ganglion neurones. In addition, some preliminary results from guinea-pig nodose ganglion neurones are presented. In such cells, voltage-clamped at -60 mV, 5-HT (10 microM) induced an inward current associated with a conductance increase. The results of ion substitution experiments suggest that the 5-HT activated ion channel is permeable to both Na+ and K+ ions with a permeability ratio (PNa/PK) of 0.94 and 0.92 for rabbit nodose ganglion cells and N1E-115 cells respectively. On outside out membrane patches excised from rabbit nodose ganglion neurones, 5-HT (1 microM) activated clearly discernible single channel currents with a conductance of 16.6 +/- 0.7 pS (n = 4). In contrast, fluctuation analysis of 5-HT induced whole cell currents suggests that the single channel conductance of N1E-115 cells is only 0.3 pS, a value some 50 fold lower. The 5-HT-induced whole cell currents recorded from all three preparations were antagonised by the selective 5-HT3 receptor antagonist ondansetron (GR38032F) and by the less selective agents metoclopramide, cocaine and (+)-tubocurarine. However, these preparations demonstrate a differential sensitivity to some antagonists. In particular, (+)-tubocurarine was a potent antagonist in N1E-115 cells (IC50 = 0.85 nM) but was approximately 200 fold (IC50 = 156 nM) and 1200 fold (IC50 = 10 microM) less potent in rabbit and guinea-pig nodose ganglion neurones respectively. Additionally, a novel effect of ketamine (10 microM) to potentiate the 5-HT-induced current of rabbit nodose ganglion neurones is described.

Action Potentials↗