Search PubMed⌕ Search

Biomedical subjects

K C Rice

Publications and source records attributed to K C Rice.

At least 253 records · Page 14Linked to original sources
PubMed1989

meta- and para-isothiocyanato-t-butylbicycloorthobenzoate: irreversible ligands of the gamma-aminobutyric acid-regulated chloride ionophore.

The meta- and para-isothiocyanato derivatives of t-butylbicycloorthobenzoate (TBOB) were synthesized by catalytic reduction of the corresponding nitro compounds, followed by treatment with thiophosgene. p-NCS-TBOB (2) inhibited the binding of both [3H]TBOB and [35S]t-butylbicyclophosphorothionate (TBPS) with potencies (IC50 of 61 and 23 nM, respectively) similar to the parent compound. In contrast, the meta derivative (m-NCS-TBOB, 1) was more than 1 order of magnitude less potent (IC50 of 1588 and 149 nM, respectively). The IC50 values for both 1 and 2 were strongly dependent on the tissue concentration, in a manner characteristic of irreversible inhibitors. Moreover, preincubation of tissue with these compounds, followed by extensive washing, resulted in a concentration-dependent reduction in the number of [35S]TBPS binding sites and in the apparent affinity of this radioligand. Similar effects were not observed in tissues treated in identical fashion with either TBOB or picrotoxin. Preincubation with p-NCS-TBOB at concentrations that significantly inhibit [35S]TBPS or [3H]TBOB binding did not affect radioligand binding to either benzodiazepine or gamma-aminobutyric acid receptors. These findings suggest that m- and p-NCS-TBOB bind irreversibly to sites labeled by cage convulsants such as TBOB and TBPS, which are on or near GABA-gated chloride channels. p-NCS-TBOB should prove useful in determining the molecular characteristics of the benzodiazepine receptor-coupled GABA-gated chloride ionophore.

Animals↗
PubMed1989

The psychotomimetic drug phencyclidine labels two high affinity binding sites in guinea pig brain: evidence for N-methyl-D-aspartate-coupled and dopamine reuptake carrier-associated phencyclidine binding sites.

Numerous studies have now demonstrated that a binding site for the psychotomimetic drug phencyclidine (PCP) exists within the receptor channel complex for the excitatory amino acid neurotransmitter glutamate, specifically the glutamate receptor selectively activated by N-methyl-D-aspartate (NMDA). Several lines of evidence support the hypothesis that all PCP receptors in rat brain are associated with the NMDA receptor complex. In the present study, we reexamine this hypothesis. We report that the PCP analog [3H]1-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) labels two high affinity binding sites in membranes prepared from guinea pig brain site 1 (Kd = 14.1 nM, Bmax = 631 fmol/mg of protein) and site 2 (Kd = 46.5 nM, Bmax = 829 fmol/mg of protein). (+)-5-Methyl-10 11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate bound to site 1 with high affinity (Kl = 3.2 nM) and to site 2 with low affinity (Kl = 5208 nM). The order of potency of drugs for inhibiting [3H]TCP binding to site 1 correlated with their ED50 values for inhibition of NMDA-mediated responses reported in the literature, whereas the order of potency of drugs for inhibiting [3H]TCP binding to site 2 correlated with their ED50 values for inhibition of [3H]dopamine reuptake reported in the literature. Kinetic experiments demonstrated that glutamate, 2-amino-7-phosphonoheptanoic acid, and Mg2+ modulated [3H]TCP binding to site 1 but not site 2. Preincubation of guinea pig striatal membranes with varying concentrations of the high affinity dopamine reuptake inhibitors N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3- phenylpropyl]piperazine caused a wash-resistant inhibition of [3H]TCP binding to site 2 but not site 1. Taken collectively, these data demonstrate the existence of a high affinity PCP binding site associated with the dopamine reuptake carrier and raise the possibility that the therapeutic and psychotomimetic effects of PCP in humans are separable and mediated via different binding sites.

Acetylcholine↗
PubMed1989

Anticonvulsant activities of 1-phenylcyclohexylamine and its conformationally restricted analog 1,1-pentamethylenetetrahydroisoquinoline.

1-Phenylcyclohexylamine (PCA), an analog of phenyclidine (PCP) in which the piperidine ring is replaced by a primary amino group, and its conformationally restricted analog 1,1-pentamethylenetetrahydroisoquinoline (PM-THIQ) were potent anticonvulsants in the mouse maximal electroshock (MES) seizure test (ED50 values, 7.0 and 14.3 mg/kg, respectively). At higher doses, the drugs caused motor impairment (TD50 values, 16.3 and 43.0 mg/kg) and blocked the behavioral effects and lethality of i.p. injected N-methyl-D-aspartate (NMDA) (ED50 values, 36.3 and 127 mg/kg). The separation in potencies in the MES seizure and motor toxicity tests of PCA and PM-THIQ contrasts with PCP which was equally potent in both tests. Several compounds that were structurally related to PM-THIQ (N-ethyl-PCA, 2-methyl-PCA, N-methyl-PM-THIQ, tetrahydroisoquinoline and benzylamine) also blocked MES seizures and caused motor impairment, but failed to show as great a separation between MES anticonvulsant activity and motor toxicity. None of the compounds protected against seizures induced by the chemoconvulsant pentylenetetrazol at doses that lacked motor toxicity. The drugs were also evaluated for their ability to displace [3H]-1-[1-(2-thienyl)-cyclohexyl]piperidine from binding to high affinity acceptor sites (presumably on NMDA receptor-coupled channels) in rat brain homogenates. The rank order of potencies in the binding assay was similar to that in the behavioral tests, except for 2-methyl-PCA which was behaviorally more potent than expected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Etoxadrol-meta-isothiocyanate: a potent, enantioselective, electrophilic affinity ligand for the phencyclidine-binding site.

Etoxadrol-meta-isothiocyanate (2S,4S,6S-2-ethyl-2-(3-isothiocyanatophenyl)-2-piperidyl)1,3-dioxolane, 4a) has been synthesized and characterized as an irreversible ligand for the phencyclidine (PCP)-binding site. It is the first chiral electrophilic affinity ligand for this site to have been described. This affinity ligand is based upon etoxadrol, a 1,3-dioxolane known to have PCP-like effects in vivo and in vitro. Etoxadrol-meta-isothiocyanate was found to be four-five times more potent in vitro than metaphit (1-[1-(3- isothiocyanatophenyl)cyclohexyl]piperidine), the only previously known electrophilic affinity ligand for the PCP-binding site. The binding was shown to be highly enantioselective for etoxadrol-meta-isothiocyanate (4a). The 2R,4R,6R-enantiomer of 4a was essentially inactive. The ability of the 2S,4S,6S-enantiomer (4a) to interact with the benzodiazepine, muscarinic, and mu opioid receptor systems was also examined, and it was found not to interact with these receptor systems. It seems likely that 4a will prove to be a valuable tool in the study of structure and function of the PCP-binding site.

Acylation↗
PubMed1988

Evidence for a delta-class opioid receptor on cells of the immune system.

Opioid receptors have been reported to be present on cells of the immune system. Both opioid receptor-ligand interactions which are reversible by naloxone (classical) and those interactions which are irreversible by naloxone (nonclassical) appear to alter various immunologic parameters through the ligand-receptor interactions. In an effort to characterize opioid receptors (which operate with classical interactions) on cells of the immune system, we employed the delta-class opioid receptor-specific ligand, cis-(+)-3-methylfentanylisothiocyanate (SUPERFIT). We herein report the specific labeling of a protein with a molecular weight of 70,000 Da under reducing conditions (58,000 Da under nonreducing conditions) from both B and T cell-enriched murine splenocytes and peripheral blood lymphocytes. Similar results are demonstrated by human peripheral blood lymphocytes and plastic-adherent (monocyte-enriched) leukocytes.

Animals↗
PubMed1988

Mu-, delta- and kappa-opioid receptor-mediated inhibition of neurotransmitter release and adenylate cyclase activity in rat brain slices: studies with fentanyl isothiocyanate.

We investigated the effects of [D-Ala2,D-Leu5]enkephalin (DADLE). [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO), [D-Pen2,D-Pen5]enkephalin (DPDPE) (0.01-1 microM) and bremazocine (0.001-0.3 microM) on the electrically evoked release of radiolabelled neurotransmitters and on the dopamine (DA)-stimulated cyclic AMP efflux from superfused rat brain slices. The differential inhibitory effects of these agonists on the evoked neurotransmitter release indicate that the opioid receptors mediating presynaptic inhibition of [3H]noradrenaline (NA, cortex), [14C]acetylcholine (ACh, striatum) and [3H]DA (striatum) release represent mu, delta and kappa receptors, respectively. In agreement with this classification, preincubation (60 min) of the slices with the delta-opioid receptor-selective irreversible ligand, fentanyl isothiocyanate (FIT, 0.01-1 microM), antagonized the inhibitory effects of DADLE and DPDPE on striatal [14C]ACh release only. On the other hand, the D-1 DA receptor-stimulated cyclic AMP efflux from striatal slices appeared to be inhibited by activation of mu as well as of delta receptors. In this case, the reversible mu antagonist, naloxone (0.1 microM), fully antagonized the inhibitory effect of the mu agonist, DAGO, without changing the effect of the delta agonist DPDPE but was ineffective as an antagonist in slices pretreated with FIT (1 microM). The inhibitory effect of DAGO on the electrically evoked [3H]NA release was antagonized by naloxone whether the receptors were irreversibly blocked by FIT or not. These data not only further support the existence of independent presynaptic mu-, delta- and kappa-opioid receptors in rat brain but also evidence strongly that mu and delta receptors mediating the inhibition of DA-sensitive adenylate cyclase could share a common binding site (for naloxone and FIT) and, therefore, may represent constituents of a functional opioid receptor complex.

Acetylcholine↗
PubMed1988

Differential regulation of mu-opiate receptors in heroin- and morphine-dependent rats.

Rats made dependent on heroin and morphine exhibit both qualitative and quantitative differences in the characteristics of radioligand binding to mu-opioid receptors in the central nervous system. In brain membranes prepared from control animals, [3H]dihydromorphine (DHM) binding was best described by a two-site model, while in morphine-dependent rats, [3H]DHM binding was best described by a single-site model. In contrast, [3H]DHM binding to membranes from heroin-dependent animals was best described by a two-site model, with an increased density of the high-affinity, and no change in the low-affinity population compared to controls. Furthermore, both the number of binding sites for [3H]DAGO (a ligand that selectively labels a population of high-affinity mu-opiate receptors) and the sensitivity of [3H]DHM to sodium ions was increased in heroin; but not in morphine-dependent rats. These studies demonstrate that opiate receptors are differentially regulated in heroin- and morphine-dependent animals. Such neurochemical changes in mu-opiate receptors may underlie differences in the behavioral and pharmacological profiles of heroin and morphine reported in man.

Animals↗
PubMed1988

Fentanyl isothiocyanate reveals the existence of physically associated mu- and delta-opioid receptors mediating inhibition of adenylate cyclase in rat neostriatum.

Dopamine D-1 receptor-stimulated cyclic AMP efflux from superfused rat neostriatal slices was strongly inhibited by the delta-opioid receptor agonist, [D-Pen2, D-Pen5]enkephalin (DPDPE, 1 microM), and by the mu-opioid receptor agonist, [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO, 1 microM). Naloxone (0.1 microM) fully antagonized the inhibitory effect of DAGO, leaving that of DPDPE virtually unchanged. Preincubation of the slices with the irreversible delta receptor ligand, fentanyl isothiocyanate (FIT, 1 microM) did not affect the inhibitory effect of DAGO, but prevented that of DPDPE. Naloxone no longer antagonized the inhibitory effect of DAGO when the delta receptors were selectively and irreversibly blocked by FIT. These data indicate that FIT and naloxone, acting on delta and mu receptors, respectively, may share a common binding site, suggesting the involvement of a functional mu, delta-opioid receptor-complex.

Adenylyl Cyclase Inhibitors↗
PubMed1988

Differential coupling of mu-competitive and mu-noncompetitive delta opiate receptors to guanine nucleotide binding proteins in rat brain membranes.

The effects of fentanyl isothiocyanate (FIT) and pertussis toxin on the binding of [3H]D-Ala2, D-Leu5-enkephalin ([3H]DADLE) to rat brain membranes were compared. The site of action of pertussis toxin was confirmed by the labeling of a 41,000 dalton protein in the presence of [alpha-32P]NAD. Both reagents produced inhibition of [3H]DADLE binding when binding was assayed in 10 mM Tris-HCl buffer alone. FIT inhibited binding 91% whereas pertussis toxin treatment resulted in 27% inhibition. However, when binding was assayed in 10 mM Tris-HCl containing SMG (100 mM NaCl, 3 mM manganese acetate, and 2 microM guanosine triphosphate), inhibition due to both reagents was attenuated markedly: 66% for FIT and 5% for toxin. In addition, both reagents markedly potentiated enhancement of binding by SMG. Thus, the effects of FIT and pertussis toxin on [3H]DADLE binding were qualitatively similar. These results suggest that FIT and pertussis toxin affect binding of [3H]DADLE to the same population of delta receptors. This was further supported by the observation that treatment of membranes with FIT prior to pertussis toxin treatment blocked the effect of toxin on [3H]DADLE binding. FIT selectively eliminates the SMG-insensitive, mu-competitive [3H]DADLE binding site [Rothman et al., Neuropeptides 4, 201 (1984); Rothman et al., Molec. Pharmac. 27, 399 (1985)]. These results indicate that this site is coupled to G protein substrates for pertussis toxin and that it mediates the inhibitory effects of delta ligands on adenylate cyclase. The FIT-insensitive, SMG-sensitive mu-noncompetitive [3H]DADLE site appears not to be coupled to G protein substrates for pertussis toxin and may mediate some other biochemical effects of delta ligands.

Adenylate Cyclase Toxin↗
PubMed1988

Chronic administration of morphine and naltrexone up-regulate[3H][D-Ala2,D-leu5]enkephalin binding sites by different mechanisms.

Previous studies have demonstrated that chronic administration of morphine up-regulated the lower affinity binding site for [3H][D-ala2,D-leu5]enkephalin, without producing a detectable alteration in the higher affinity binding site for [3H][D-ala2,D-leu5]enkephalin (Rothman et al., Eur. J. Pharmac. 124: 113-119, 1986). The experiments reported in this paper tested the hypothesis that chronic administration of morphine and naltrexone up-regulated the binding sites for [3H][D-ala2,D-leu5]enkephalin by different mechanisms. Rats were given either morphine or naltrexone chronically. Chronic administration of morphine up-regulated the lower affinity site, while chronic administration of naltrexone up-regulated both the higher and lower affinity binding sites for [3H][D-ala2,D-leu5]enkephalin. Unlike the lower affinity binding site for [3H][D-ala2,D-leu5]enkephalin present in membranes prepared from rats treated with placebo pellets, the lower affinity binding sites which were up-regulated by naltrexone and morphine were partially (naltrexone) or completely (morphine) labile to preincubation for 60 min at 25 degrees C in 50 mM Tris-HCl, pH 7.4, containing 0.4 M NaCl. These data suggest that chronic administration of morphine and naltrexone up-regulate binding sites for [3H][D-ala2,D-leu5]enkephalin through different mechanisms, and that the lower affinity binding sites for [3H][D-ala2, D-leu5]enkephalin which are up-regulated by chronic administration of morphine and naltrexone might differ biochemically from the lower affinity binding sites present in membranes treated with placebo.

Animals↗