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A P Hill

Publications and source records attributed to A P Hill.

18 recordsLinked to original sources
PubMed2006

Effect of S5P alpha-helix charge mutants on inactivation of hERG K+ channels.

The ether-à-go-go (EAG) family of voltage-gated K(+) channels contains three subfamilies, EAG, ether-à-go-go related (ERG) and ether-à-go-go like (ELK). The human ether-à-go-go related gene (hERG) K(+) channel has been of significant interest because loss of function in the hERG channel is associated with a markedly increased risk of cardiac arrhythmias. The hERG channel has unusual kinetics with slow activation and deactivation but very rapid and voltage-dependent inactivation. The outer pore region of the hERG K(+) channel is predicted to be different from that of other members of the voltage-gated K(+) channel family. HERG has a much longer linker between the fifth transmembrane domain (SS) and the pore helix (S5P linker) compared to other families of voltage-gated K(+) channels (43 amino acids compared to 14-23 amino acids). Further, the S5P linker contains an amphipathic alpha-helix that in hERG channels probably interacts with the mouth of the pore to modulate inactivation. The human EAG and rat ELK2 channels (hEAG and rELK2) show reduced or no inactivation in comparison to hERG channels, yet both channels are predicted to contain a similarly long S5P linker to that of hERG. In this study, we have constructed a series of chimaeric channels consisting of the S1-S6 of hERG but with the S5P alpha-helical region of either hEAG or rELK2, and one consisting of the S1-S6 of rELK2 but with the S5P alpha-helical region of hERG to investigate the role of the S5P linker in inactivation. Our studies show that charged residues on the alpha-helix of the S5P linker contribute significantly to the differences in inactivation characteristics of the EAG family channels. Further, individually mutating each of the hydrophilic residues on the S5P alpha-helix of hERG to a charged residue had significant effects on the voltage dependence of inactivation and the two residues with the greatest affect when mutated to a lysine, N588 and Q592, both lie on the same face of the S5P alpha -helix. We suggest that inactivation of hERG involves the interaction of this face of the S5P alpha-helix with a charged residue on the remainder of the outer pore domain of the channel.

Animals↗
PubMed2001

Retention of ionizable compounds on HPLC. 8. Influence of mobile-phase pH change on the chromatographic retention of acids and bases during gradient elution.

The relationships between retention and mobile-phase pH in gradient elution are studied for acids and bases. The apparent pH shift caused by the increasing amount of acetonitrile and methanol has been determined starting from a wide range of pH values. It is shown that good relationships between the retention of ionizable compounds and the pH of the aqueous buffer can be established if the same type of buffer (ammonium acetate in this work) is used for all pH points. Equations are proposed to fit the gradient retention data to the pH of the aqueous buffer. The proposed equation gives an account of the relative variation of the pKa of the compound in the reference to the variation of the pH of the buffer as both parameters change during gradient elution.

Acetic Acid↗
PubMed2001

Discovery of 4-[3-(trans-3-dimethylaminocyclobutyl)-1H-indol-5-ylmethyl]-(4S)-oxazolidin-2-one (4991W93), a 5HT(1B/1D) receptor partial agonist and a potent inhibitor of electrically induced plasma extravasation.

Utilizing a pharmacophoric model of binding of 3-(2-aminoethyl)indoles to 5HT(1B/1D) receptors, we identified the 3-aminocyclobutyl group as a potential ethylamine isostere. A novel multidimensional chemometric approach was used to predict the intrinsic activity (degree of agonism) at the receptor. A qualitative model for pharmacokinetic properties was then used to guide the synthesis toward molecules likely to have oral bioavailability in humans. A novel synthetic route to 3-(3-dimethylaminocyclobutyl)indoles was developed. Analogues showed generally lower intrinsic activity at 5HT(1B/1D) receptors than their ethylamine counterparts. 4-[3-(trans-3-Dimethylaminocyclobutyl)-1H-indol-5-ylmethyl]-(4S)-oxazolidin-2-one (4991W93, 1) was identified as a partial agonist against 5HT(1B/1D) receptors, with low intrinsic activity. This molecule also has significant activity against 5HT(1F) receptors but is selective over other 5HT receptors. In addition this compound was found to be an exceptionally potent inhibitor of electrically induced plasma extravasation. Compound 1 may have utility in the treatment and prophylaxis of migraine.

Administration, Oral↗
PubMed2001

Characterization and purification of the vitamin K1 2,3 epoxide reductases system from rat liver.

The enzyme vitamin K1 2,3 epoxide reductase is responsible for converting vitamin K1 2,3 epoxide to vitamin K1 quinone thus completing the vitamin K cycle. The enzyme is also the target of inhibition by the oral anticoagulant, R,S-warfarin. Purification of this protein would enable the interaction of the inhibitor with its target to be elucidated. To date a single protein possessing vitamin K1 2,3 epoxide reductase activity and binding R,S-warfarin has yet to be purified to homogeneity, but recent studies have indicated that the enzyme is in fact at least two interacting proteins. We report on the attempted purification of the vitamin K1 2,3 epoxide reductase complex from rat liver microsomes by ion exchange and size exclusion chromatography techniques. The intact system consisted of a warfarin-binding factor, which possessed no vitamin K1 2,3 epoxide reductase activity and a catalytic protein. This catalytic protein was purified 327-fold and was insensitive to R,S-warfarin inhibition at concentrations up to 5 mM. The addition of the S-200 size exclusion chromatography fraction containing the inhibitor-binding factor resulted in the return of R,S-warfarin inhibition. Thus, to function normally, the rat liver endoplasmic reticulum vitamin K1 2,3 epoxide reductase system requires the association of two components, one with catalytic activity for the conversion of the epoxide to the quinone and the second, the inhibitor binding factor. This latter enzyme forms the thiol-disulphide redox centre that in the oxidized form binds R,S-warfarin.

Animals↗
PubMed1998

Oral pessimism and depressive symptoms: a comparison with other correlates of depression.

The need to examine alternative explanations for findings in psychoanalytic theory is often suggested but rarely practised. The aim of the present study was to examine Lewis' (1993) prediction that oral pessimism is important to the aetiology of depression within the context of social psychological, cognitive and personality explanations of depression. One hundred and sixty Northern Irish university students completed measures of depressive symptoms, oral pessimism and oral optimism, optimism, neuroticism, coping style, attribution style and self-esteem. Results show that oral pessimism, neuroticism and the use of stable attributions are dominant in accounting for variance in a measure of depression and support Lewis' (1993) finding that oral pessimism is important in depressive symptoms.

Adolescent↗
PubMed1997

Chemical, spectroscopic and structural investigation of the substrate-binding site in ascorbate peroxidase.

The interaction of recombinant ascorbate peroxidase (APX) with its physiological substrate, ascorbate, has been studied by electronic and NMR spectroscopies, and by phenylhydrazine-modification experiments. The binding interaction for the cyanide-bound derivative (APX-CN) is consistent with a 1:1 stoichiometry and is characterised by an equilibrium dissociation binding constant. Kd, of 11.6 +/- 0.4 microM (pH 7.002, mu = 0.10 M, 25.0 degrees C). Individual distances between the non-exchangeable substrate protons of APX-CN and the haem iron were determined by paramagnetic-relaxation NMR measurements, and the data indicate that the ascorbate binds 0.90-1.12 nm from the haem iron. The reaction of ferric APX with the suicide substrate phenylhydrazine yields predominantly (60%) a covalent haem adduct which is modified at the C20 carbon, indicating that substrate binding and oxidation is close to the exposed C20 position of the haem, as observed for other classical peroxidases. Molecular-modelling studies, using the NNM-derived distance restraints in conjunction with the crystal structure of the enzyme [Patterson, W. R. & Poulos, T. L. (1995) Biochemistry 34, 4331-4341], are consistent with binding of the substrate close to the C20 position and a possible functional role for alanine 134 (proline in other class-III peroxidases) is implicated.

Ascorbate Peroxidases↗
PubMed1995

Computer-aided design and synthesis of 5-substituted tryptamines and their pharmacology at the 5-HT1D receptor: discovery of compounds with potential anti-migraine properties.

The design and synthesis of a series of novel 5-substituted tryptamines with pharmacological activity at 5-HT1D and other monoamine receptors is described. Structural modifications of N- and C-linked (principally hydantoin) analogues at the 5-position were synthesized and their pharmacological activities were utilized to deduce significant steric and electrostatic requirements of the 5-HT1D and 5-HT2A receptor subtypes. Conformations of the active molecules were computed which, when overlaid, suggested a pharmacophore hypothesis which was consistent with the affinity and selectivity measured at 5-HT1D and 5-HT2A receptors. This pharmacophore is composed of a protonated amine site, an aromatic site, a hydrophobic pocket, and two hydrogen-bonding sites. A "selectivity site" was also identified which, if occupied, induced sensitivity for 5-HT1D over 5-HT2A in this series of molecules. The development and use of the pharmacophore models in compound design is described. In addition, the physicochemical constraints of molecular size and hydrophobicity required for efficient oral absorption are discussed. Utilizing the pharmacophore model in conjunction with the physicochemical constraints of molecular size and log DpH7.4 led to the discovery of 311C90 (6), a new selective 5-HT1D agonist with good oral absorption and potential use in the treatment of migraine.

Animals↗
PubMed1992

Targeting asthma care in general practice using a morbidity index.

OBJECTIVES: To evaluate a morbidity index as a postal surveillance tool in defining previously diagnosed asthmatic patients needing extra education or management; to determine the accuracy of a computerised asthma register in general practice. DESIGN: Postal questionnaire survey of asthmatic patients identified from a computer register. Questionnaire comprised three morbidity questions, two questions about current asthma status, and one about treatments. SETTING: Urban general practice of 8400 patients linked to academic unit. SUBJECTS: 853 asthmatic patients of all ages. MAIN OUTCOME MEASURES: Numbers of patients with low, medium, and high morbidity; associations of these groups with age, asthma status, and drugs taken. RESULTS: Two mailings yielded 621 replies (73%); 28 patients (5%) had moved away, leaving 593 for analysis. Attempts were subsequently made to contact 20% sample of non-respondents. 234 respondents (40%) were in the "low morbidity" group, 149 (25%) in the "medium morbidity" group, and 210 (35%) in the "high morbidity" category. 53% of patients perceiving themselves as currently asthmatic (193/362) were in the high morbidity group, but 7% (11/153) who said they were no longer asthmatic and 8% (6/78) who did not believe they had ever been asthmatic were also in that group. High morbidity was also found in 10% (18/185) of those on no treatment, 38% (59/154) of those on bronchodilators alone, and 54% (119/220) of those on inhaled corticosteroids. 25 patients (4%) were wrongly identified as asthmatic; when combined with returns marked "gone away" this gave a disease register accuracy of 91%. CONCLUSIONS: This exercise identified subgroups of previously diagnosed asthmatic patients with high morbidity in general practice who might benefit from extra education and management and revealed some misclassification on the asthma disease register.

Asthma↗
PubMed1990

Cardiotonic 'C' ring modified isomazole analogues.

Isomazole analogues which have achiral electron withdrawing substituents at the 4'-position and analogues with heterocyclic 'C' rings have been synthesized and evaluated as inotropic agents. It was found that pyridyl could replace phenyl in the 'C' ring without loss of activity. The 4'-methylsulphonyl, -cyano, -carboxamido, and acetyl analogues had similar inotropic potencies to Isomazole whilst displaying superior cardiovascular profiles in in vivo studies.

Animals↗
PubMed1990

Inotropic "A" ring substituted sulmazole and isomazole analogues.

A series of "A" ring substituted sulmazole and isomazole analogues have been prepared and evaluated as inotropic agents. pKA's, protonation sites, and log P values were measured for selected compounds and their electronic properties were calculated. No simple correlation between inotropic activity and pKA, protonation site, or log P value was observed. However, in vitro inotropism did correlate with the calculated charge density of the "B" ring imidazo nitrogen atom. The 6-position of sulmazole appeared to be the most tolerant toward substituents, the 6-amino derivative 7 being a more potent inotrope than sulmazole itself. 4-Methoxyisomazole 13 had comparable in vivo inotropic properties to those of isomazole.

Animals↗
PubMed1980

Bias and efficiency in logistic analyses of stratified case-control studies.

Two approaches to the estimation of the parameters in the logistic model applied to the analysis of stratum matched case-control studies are compared. It is shown that the "unconditional likelihood method' gives estimates of odds ratios which may be severely exaggerated if the stratum sizes are not large; however, if stratum sizes are not small the "conditional likelihood method' is computationally prohibitive. The use of small stratum sizes (e.g., 1-to-1 matching) leads to some loss of efficiency if the matching is irrelevant but it is shown that the loss is small for odds ratios up to at least 3. There would seem to be strong arguments for the routine use of matched designs as the reduction in confounding bias produced by such matching may be considerable whereas there is only a small loss in efficiency compared with unmatched designs.

Humans↗
PubMed1979

Epidemiology of hepatocellular adenoma. The role of oral contraceptive use.

A case-control study of hepatocellular adenoma (HCA), a serious though nonmalignant liver tumor, was conducted by the Center for Disease Control and the Armed Forces Institute of Pathology (AFIP). Interviews with 79 women with HCA and with 220 age- and neighborhood-matched controls were completed. Limited information was obtained on nine additional patients who had died. Women with HCA and hemorrhage have a greater risk of morbidity and death than those with other symptoms. Increasing duration of OC use increases the risk of HCA. Use of OCs with high hormonal potency and age over 30 years may further increase a woman's risk of HCA. Long-term users of OCs have an estimated annual incidence of HCA of 3 to 4 per 100,000.

Adolescent↗
PubMed1975

Quantitative linkage: a statistical procedure for its detection and estimation.

A new approach for detecting and estimating quantitative linkage which uses sibship data is presented. Using a nested analysis of variance design (with marker genotype nested within sibship), it is shown that under the null hypothesis of no linkage, the expected between marker genotype within sibship mean square (EMSbeta) is equal to the expected within marker genotype within sibship mean square (EMSe), while under the alternative hypothesis of linkage, the first is greater than the second. Thus the regular F-ratio, MSbeta/MSe, can be used to test for quantitative linkage. This is true for both backcross and intercross matings and whether or not there is dominance at the marker locus. A second test involving the comparison of the within marker genotype within sibship variances is available for intercross matings. A maximum likelihood procedure for the estimation for the recombination frequency is also presented.

Alleles↗