PubMed Health⌕ Search

Biomedical subjects

R J Mather

Publications and source records attributed to R J Mather.

11 recordsLinked to original sources
PubMed2006

Pharmacological profile of the alpha4beta2 nicotinic acetylcholine receptor partial agonist varenicline, an effective smoking cessation aid.

The preclinical pharmacology of the alpha4beta2 nicotinic acetylcholine receptor (nAChR) partial agonist varenicline, a novel smoking cessation agent is described. Varenicline binds with subnanomolar affinity only to alpha4beta2 nAChRs and in vitro functional patch clamp studies in HEK cells expressing nAChRs show that varenicline is a partial agonist with 45% of nicotine's maximal efficacy at alpha4beta2 nAChRs. In neurochemical models varenicline has significantly lower (40-60%) efficacy than nicotine in stimulating [(3)H]-dopamine release from rat brain slices in vitro and in increasing dopamine release from rat nucleus accumbens in vivo, while it is more potent than nicotine. In addition, when combined with nicotine, varenicline effectively attenuates the nicotine-induced dopamine release to the level of the effect of varenicline alone, consistent with partial agonism. Finally, varenicline reduces nicotine self-administration in rats and supports lower self-administration break points than nicotine. These data suggest that varenicline can reproduce to some extent the subjective effects of smoking by partially activating alpha4beta2 nAChRs, while preventing full activation of these receptors by nicotine. Based on these findings, varenicline was advanced into clinical development and recently shown to be an effective and safe aid for smoking cessation treatment.

Animals↗
PubMed1999

Cloning, structural characterization, and chromosomal localization of the gene encoding the human prostaglandin E(2) receptor EP2 subtype.

Northern blot analysis of human placental RNA using a probe to the 5' end of the human prostaglandin E(2) (PGE(2)) EP2 receptor subtype coding region revealed the existence of a high abundance, low molecular weight transcript. To investigate the origin of this transcript, and its possible relationship to the human EP2 mRNA, we have cloned and characterized the gene encoding the human PGE(2) EP2 receptor subtype, identified transcriptional initiation and termination sites in two tissues (spleen and thymus), and determined its chromosomal localization. The human EP2 gene consists of two exons separated by a large intron, utilizes a common initiation site in both spleen and thymus at 1113 bp upstream of the translation initiation site, and has 3' transcript termini at 1140 bp and 1149 bp downstream of the translation stop site in spleen and thymus respectively. Southern and fluorescence in situ hybridization analysis demonstrated the human EP2 gene to be a single copy gene located in band 22 of the long arm of chromosome 14 (14q22). Though our initial interest in this gene was to investigate potential differential splicing of the human EP2 gene in placenta, this work demonstrates that the atypical transcript observed in placenta probably arises from a distinct, yet related, gene. Knowledge of the sequence, structure, and transcription events associated with the human EP2 gene will enable a broader understanding of its regulation and potential role in normal physiology and disease.

Amino Acid Sequence↗
PubMed1999

UK-78,282, a novel piperidine compound that potently blocks the Kv1.3 voltage-gated potassium channel and inhibits human T cell activation.

1. UK-78,282, a novel piperidine blocker of the T lymphocyte voltage-gated K+ channel, Kv1.3, was discovered by screening a large compound file using a high-throughput 86Rb efflux assay. This compound blocks Kv1.3 with a IC50 of approximately 200 nM and 1:1 stoichiometry. A closely related compound, CP-190,325, containing a benzyl moiety in place of the benzhydryl in UK-78,282, is significantly less potent. 2 Three lines of evidence indicate that UK-78,282 inhibits Kv1.3 in a use-dependent manner by preferentially blocking and binding to the C-type inactivated state of the channel. Increasing the fraction of inactivated channels by holding the membrane potential at - 50 mV enhances the channel's sensitivity to UK-78,282. Decreasing the number of inactivated channels by exposure to approximately 160 mM external K+ decreases the sensitivity to UK-78,282. Mutations that alter the rate of C-type inactivation also change the channel's sensitivity to UK-78,282 and there is a direct correlation between tau(h) and IC50 values. 3. Competition experiments suggest that UK-78,282 binds to residues at the inner surface of the channel overlapping the site of action of verapamil. Internal tetraethylammonium and external charybdotoxin do not compete UK-78,282's action on the channel. 4. UK-78,282 displays marked selectivity for Kv1.3 over several other closely related K+ channels, the only exception being the rapidly inactivating voltage-gated K+ channel, Kv1.4. 5. UK-78,282 effectively suppresses human T-lymphocyte activation.

Animals↗
PubMed1996

Novel nonpeptide agents potently block the C-type inactivated conformation of Kv1.3 and suppress T cell activation.

The nonpeptide agent CP-339,818 (1-benzyl-4-pentylimino-1,4-dihydroquinoline) and two analogs (CP-393,223 and CP-394,322) that differ only with respect to the type of substituent at the N1 position, potently blocked the Kv1.3 channel in T lymphocytes. A fourth compound (CP-393,224), which has a smaller and less-lipophilic group at N1, was 100-200-fold less potent, suggesting that a large lipophilic group at this position is necessary for drug activity. CP-339,818 blocked Kv1.3 from the outside with a IC50 value of approximately 200 nM and 1:1 stoichiometry and competitively inhibited 125I-charybdotoxin from binding to the external vestibule of Kv1.3. This drug inhibited Kv1.3 in a use-dependent manner by preferentially blocking the C-type inactivated state of the channel. CP-339,818 was a significantly less potent blocker of Kv1.1, Kv1.2, Kv1.5, Kv1.6, Kv3.1-4, and Kv4.2; the only exception was Kv1.4, a cardiac and neuronal A-type K+ channel. CP-339,818 had no effect on two other T cell channels (I(CRAC) and intermediate-conductance K(Ca)) implicated in T cell mitogenesis. This drug suppresses human T cell activation, suggesting that blockade of Kv1.3 alone is sufficient to inhibit this process.

HeLa Cells↗
PubMed1994

Pharmacological characterization of five cloned voltage-gated K+ channels, types Kv1.1, 1.2, 1.3, 1.5, and 3.1, stably expressed in mammalian cell lines.

We have analyzed the biophysical and pharmacological properties of five cloned K+ (Kv) channels (Kv1.1, Kv1.2, Kv1.3, Kv1.5, and Kv3.1) stably expressed in mammalian cell lines. Kv1.1 is biophysically similar to a K+ channel in C6 glioma cells and astrocytes, Kv1.3 and Kv3.1 have electrophysiological properties identical to those of the types n and l K+ channels in T cells, respectively, and Kv1.5 closely resembles a rapidly activating delayed rectifier in the heart. Each of these native channels may be formed from the homomultimeric association of the corresponding Kv subunits, and pharmacological compounds that selectively modulate them may be useful for the treatment of neurological, immune, and cardiac disorders. The cell lines described in this report could be used to identify such drugs and we have therefore embarked on a pharmacological characterization of the five cloned channels. The compounds tested in this study include 4-aminopyridine, capsaicin, charybdotoxin, cromakalim, dendrotoxin, diltiazem, D-sotalol, flecainide, kaliotoxin, mast cell degranulating peptide, nifedipine, noxiustoxin, resiniferatoxin, and tetraethylammonium.

3T3 Cells↗
PubMed1992

Intracellular guanosine-5'-O-(2-thiodiphosphate) alters the dynamics of receptor-mediated responses in bullfrog sympathetic neurons.

The mechanism by which intracellularly applied guanosine-5'-O-(2-thiodiphosphate) alters responses to chicken II luteinizing hormone-releasing hormone, muscarine, and substance P in bullfrog sympathetic neurons was examined. Whole-cell recordings were made from enzymatically dissociated single neurons. Guanosine-5'-O-(2-thiodiphosphate) was applied intracellularly by adding it to the pipette solution with fixed amounts of GTP. Guanosine-5'-O-(2-thiodiphosphate) did not affect the proportion of cells that responded to any of the agonists. Guanosine-5'-O-(2-thiodiphosphate) decreased the amplitude of the responses to submaximal concentrations of agonist. At maximal concentrations of agonist, guanosine-5'-O-(2-thiodiphosphate) did not decrease the response to the first application of agonist; however, with guanosine-5'-O-(2-thiodiphosphate) intracellularly, successive responses to maximal concentrations of agonist were decreased in amplitude and increased in time course. Intracellular guanosine-5'-O-(2-thiodiphosphate) did not accelerate the rate or magnitude of desensitization to substance P. A kinetic model of receptor-guanine nucleotide-binding protein (G protein) coupling predicts that a decrease in the available G protein pool should decrease both the magnitude and the time course of the build-up of active G proteins. The results are consistent with the hypothesis that guanosine-5'-O-(2-thiodiphosphate) binds tightly to G proteins, thereby effectively decreasing the available G protein pool with repeated agonist applications.

Animals↗
PubMed1991

Muscarinic suppression of the M-current is mediated by a rise in internal Ca2+ concentration.

The role of intracellular Ca2+ in the muscarinic suppression of M-current was examined. Intracellular injection of Ca2+ buffer into cells in the intact ganglion reduced the response to muscarinic agonist. In similar experiments on isolated cells, Ca2+ buffer was introduced into the cytoplasm using a perfused recording pipette. Ca2+ buffer (20 mM) with the free Ca2+ concentration set to normal resting levels produced a reversible reduction of the muscarinic response. In a second line of investigation, it was found that pharmacological procedures designed to deplete internal stores of Ca2+ produced a decrease in the muscarinic response. These results, taken together with previous work, support the hypothesis that the muscarinic suppression of M-current is mediated by the release of Ca2+ from intracellular stores.

Animals↗
PubMed1991

Selectivity of the effects of guanosine-5'-O-(2-thiodiphosphate) on agonist inhibition of the M-current in amphibian sympathetic neurons.

In bullfrog sympathetic neurons, luteinizing hormone-releasing hormone, muscarine, and substance P act as agonists at specific membrane receptors to decrease a potassium current, IM. The receptors are coupled to guanine nucleotide-binding proteins (G-proteins). Whole-cell recordings of IM were made from isolated bullfrog sympathetic neurons to examine the effects of intracellularly applied guanosine-5'-O-(2-thiodiphosphate) (GDP beta S) on agonist inhibition of IM. Successive responses to a given agonist were decreased in the presence of GDP beta s. Subsequent responses to the other agonists were then measured to determine the degree of overlap of the effect of GDP beta S for the different agonists. GDP beta S selectively inhibited successive responses to one agonist such that a subsequent application of a different agonist was still effective. If GDP beta S acts at the level of the G-protein, this suggests that each receptor is coupled to a separate population of G-proteins. Alternatively, GDP beta S may act at the receptor level to block receptor coupling to IM.

Animals↗
PubMed1990

Desensitization of the inhibition of the M-current in sympathetic neurons: effects of ATP analogs, polyanions, and multiple agonist applications.

Desensitization occurs when the response to a neurotransmitter receptor agonist wanes in the continued presence of agonist. In amphibian sympathetic neurons, both muscarinic and peptidergic receptor agonists inhibit a K+ current, the M-current (IM), and this inhibition desensitizes. We have studied the desensitization to substance P (SP) by whole-cell recordings from dissociated sympathetic neurons from bullfrogs. When ATP in the recording pipette was replaced with AMP-PNP, SP still inhibited IM, but no desensitization was observed, indicating that ATP hydrolysis is required for desensitization. Desensitization inhibitors of beta-adrenergic receptors did not block desensitization to SP. When a low dose of muscarine sufficient to inhibit IM, but not to elicit desensitization, was applied simultaneously with a desensitizing dose of SP, IM remained depressed and did not desensitize. Thus, there may be separate systems controlling desensitization for different agonists, or the enzyme(s) involved is "compartmentalized."

Adenosine Triphosphate↗