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K C Rice

Publications and source records attributed to K C Rice.

At least 325 records · Page 18Linked to original sources
PubMed1985

Radiosynthesis of [18F]3-acetylcyclofoxy: a high affinity opiate antagonist.

A convenient method for the preparation of high specific activity [18F]3-acetylcyclofoxy (3-acetyl-6-deoxy-6-beta-18F-fluoronaltrexone) was developed. The method utilizes reactor-produced [18F]-fluoride as its tetraethylammonium (TEA X F) salt in a SN2 displacement on a secondary triflate precursor. Typically, 45% of the 18F activity can be converted to the reactive TEAF in a 70 min preparation. From this, 35% yield (decay corrected) of the [18F]3-acetylcyclofoxy was obtained after HPLC purification with a specific activity of 25 Ci/mmol in a total synthesis time of 60 min.

Animals↗
PubMed1985

Leucine enkephalin noncompetitively inhibits the binding of [3H]naloxone to the opiate mu-recognition site: evidence for delta----mu binding site interactions in vitro.

Using quantitative methods, this study examined the hypothesis that delta-ligands are noncompetitive inhibitors at a population of mu-binding sites. Evidence is presented that with the defined set of in vitro assay conditions utilized, [3H]naloxone labels two binding sites: the mu binding site and a second site tentatively identified as a kappa binding site, and that leucine enkephalin is a noncompetitive inhibitor at the mu recognition site.

Animals↗
PubMed1985

Local anesthetic properties of opioids and phencyclidines: interaction with the voltage-dependent, batrachotoxin binding site in sodium channels.

[3H]Batrachotoxinin-A 20-alpha-benzoate ([3H]BTX-B) binds specifically and with high affinity (Kd = 30 nM) to a site on voltage-dependent Na+ channels. Compounds with local anesthetic activity inhibit the binding of [3H]BTX-B by a mutually exclusive, allosteric mechanism. The potential local anesthetic potency of a series of 23 opioids and phencyclidine-like compounds has been estimated by their inhibition of [3H]BTX-B binding to Na+ channels in a preparation of synaptoneurosomes from guinea pig cerebral cortex. The potency of these compounds were also tested as inhibitors of the specific binding of [3H]phencyclidine ([3H]PCP) to a high affinity site on rat brain membranes. Opioids such as morphine and codeine show little affinity for the [3H]BTX-B binding site or for the [3H]PCP binding site. Other analgesics, many of the PCP-like compounds and dioxadrol derivatives are potent versus [3H]BTX-B binding and display both stereospecificity and high affinity towards the PCP-binding site. However, there was no correlation between local anesthetic potency assessed as antagonism of [3H]BTX-B binding and affinity towards the PCP site. Five classical local anesthetics had no affinity for the PCP-site, but did displace [3H]BTX-B from its binding site.

Anesthetics, Local↗
PubMed1985

Evidence that the delta-selective alkylating agent, fit, alters the mu-noncompetitive opiate delta binding site.

Considerable evidence supports the notion that the prototypic delta agonist [3H]D-ala2-D-leu5-enkephalin labels two binding sites on brain membranes in vitro. Recent studies have demonstrated that treatment of brain membranes with the delta-selective, site-directed, alkylating agent, FIT (Rice et al., Science 220, 314-316, 1983) results in a membrane preparation devoid of detectable higher affinity [3H]D-ala2-D-leu5-enkephalin binding sites, but contain residual lower affinity binding sites at which mu-ligands are apparent noncompetitive inhibitors (Rothman et al., Neuropeptides 4:210-215, 1984). In this paper we extend these data by showing that although FIT eliminates the higher affinity binding site, it also alters the properties of the residual lower affinity binding sites.

Affinity Labels↗
PubMed1985

Increased affinity of dimeric enkephalins is not dependent on receptor density.

The equilibrium binding and dissociation kinetics of the enkephalin dimer bis-(D-Ala2-D-Leu5-enkephalin)-ethylenediamide (designated DPE2) to neuroblastoma glioma NG108-15 cells were investigated and compared with the monomers D-Ala2-D-Leu5-enkephalin (DADL) and D-Ala2-Leu5-enkephalinamide (DALEA). Binding was studied after exposure of the membrane to increasing concentrations of the irreversible delta receptor selective ligand FIT in order to decrease the density of binding sites on the cell membrane. The increased affinity of DPE2 did not revert to that of the monomer DADL by this reduction of binding sites. Similarly, the dissociation of DPE2 did not approach that of the monomer DALEA in the presence of 1 microM DALEA. These data strongly suggest that crosslinking does not occur, and fail to confirm the hypothesis that dimers with short spanning chain length aid the clustering of receptors. We postulate: 1) If the dimer binds to a bivalent binding site, the monovalent binding state of our bivalent ligand may not exist to an appreciable extent, and 2) the bivalent ligand cannot bind when the binding site is irreversibly blocked by a monovalent ligand.

Animals↗
PubMed1985

Preparation of rat brain membranes highly enriched with opiate kappa binding sites using site-directed acylating agents: optimization of assay conditions.

The goal of this study was to determine optimal conditions with which to measure opiate kappa binding sites in rat brain. Membranes were pretreated with mu-selective (BIT) and delta-selective (FIT) site-directed acylating agents (Rice et al., Science 220, 314-316), and the binding of [3H]bremazocine to the residual binding sites was defined as the kappa binding site. The binding of [3H]bremazocine to BIT/FIT-treated membranes was greatly increased by conducting the assay at 0 degrees C in the presence of 0.4 M NaCl. Using this 0 degrees C/NaCl assay condition, the binding of [3H]bremazocine was best described by a one-site binding model with a KD of 0.45 nM and a Bmax of 378 fmol/mg protein. Autoradiographic studies demonstrated that, using this assay condition, [3H]bremazocine densely labeled the deep layers of guinea pig cortex, an area known to be enriched with kappa binding sites. These and additional data suggest that the binding of [3H]bremazocine to the kappa binding site of rat brain is optimally assayed at 0 degrees C in the presence of 0.4 M NaCl using BIT/FIT-treated membranes and that rat brain is endowed with a high level of kappa binding sites.

Alkylating Agents↗
PubMed1985

Purification of the opiate receptor of NG108-15 neuroblastoma-glioma hybrid cells.

Opiate receptors from NG108-15 neuroblastoma-glioma hybrid cell membranes were purified to apparent homogeneity in a form covalently labeled with the opiate affinity ligand 3-methylfentanylisothiocyanate (super-FIT). The purification procedure consists of five steps: quantitative labeling of opiate receptors in membranes with super-FIT; solubilization in a lubrol/3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate mixture; adsorption to and elution from a wheat germ agglutinin-Sepharose column; immunoaffinity chromatography on columns of immobilized anti-fentanyl; preparative gel electrophoresis in the presence of NaDodSO4. The protein was purified approximately 30,000-fold in 3% overall yield to a state in which there is 1 mol of super-FIT bound per mol of protein, corresponding to 21,000 pmol per mg of protein, the theoretically expected specific activity. The protein is glycosylated and migrates on NaDodSO4 gel electrophoresis with a Mr near 58,000. It has a strong tendency to dimerize, even in the presence of denaturing detergents, and it exists primarily as an oligomer in nondenaturing detergents.

Affinity Labels↗
PubMed1985

[3H]Threo-(+/-)-methylphenidate binding to 3,4-dihydroxyphenylethylamine uptake sites in corpus striatum: correlation with the stimulant properties of ritalinic acid esters.

Saturable and stereoselective binding sites for [3H]threo-(+/-)-methylphenidate were characterized in rat brain membranes. The highest density of [3H]threo-(+/-)-methylphenidate binding sites was found in the synaptosomal fraction of corpus striatum. Scatchard analysis revealed a single class of noninteracting binding sites with an apparent dissociation constant (KD) of 235 nM and a maximum number of binding sites (Bmax) of 13.4 pmol/mg protein. Saturable, high-affinity binding of [3H]threo-(+/-)-methylphenidate to striatal synaptosomal membranes was dependent on the presence of sodium ions. A good correlation (r = 0.88; p less than 0.001) was observed between the potencies of various psychotropic drugs in displacing [3H]threo-(+/-)-methylphenidate from these sites and their potencies as inhibitors of [3H]3,4-dihydroxyphenylethylamine ( [3H]dopamine) uptake into striatal synaptosomes. A good correlation (r = 0.85; p less than 0.001) was also observed between the potencies of a series of ritalinic acid esters in inhibiting [3H]threo-(+/-)-methylphenidate binding to striatal synaptosomal membranes and their potencies as motor stimulants in mice. These observations suggest that the binding sites for [3H]threo-(+/-)-methylphenidate described here are associated with a dopamine uptake or transport complex, and that these sites may mediate the motor stimulant properties of ritalinic acid esters such as methylphenidate.

Animals↗
PubMed1985

A quantitative study of [3H]D-Ala2-D-Leu5-enkephalin binding to rat brain membranes. Evidence that oxymorphone is a noncompetitive inhibitor of the lower affinity delta-binding site.

The mechanism by which mu ligands inhibit the binding of prototypic delta agonists to preparations of brain membranes is controversial. Most investigators assume competitive inhibition. In this study, we examine the interaction of the mu agonist oxymorphone and delta agonist DSTLE (D-Ser2-Thr6-Leu-enkephalin) with [3H]D-Ala2-D-Leu5-enkephalin (DADL) binding to membranes of rat brain. According to the two-site competitive model, mu ligands are competitive inhibitors at both sites. The two-site allosteric model supposes that mu ligands are competitive inhibitors at one binding site, and noncompetitive inhibitors at the other binding site. Quantitative analysis of DSTLE and oxymorphone binding demonstrated that the two-site allosteric model fit the data significantly better than did the two-site competitive model, and that oxymorphone is a noncompetitive inhibitor of the lower affinity [3H]DADL-binding site. Autoradiographic studies demonstrated that the lower affinity [3H]DADL-binding site (mu-noncompetitive binding site) had an anatomical distribution apparently indistinguishable from that obtained with [3H]oxymorphone (type I pattern), supporting the hypothesis that the lower affinity delta-binding site is the delta-binding site of an opiate receptor complex consisting of interacting mu- and delta-binding sites.

Animals↗
PubMed1985

Effects of metaphit, a proposed phencyclidine receptor acylator, on catalepsy in pigeons.

Metaphit, a derivative of phencyclidine (PCP), irreversibly binds to PCP sites in rat brain homogenates. PCP-induced catalepsy in pigeons, which is a pharmacologically specific and stereoselective phenomenon, was used to study pharmacological consequences of the proposed covalent bonding of metaphit to PCP sites. Metaphit pretreatment increased the cataleptic effects induced by cumulative doses of PCP-type drugs (i.e., PCP, ketamine and m-amino PCP) and of drugs that have PCP-like actions (i.e., dexoxadrol, LY 154716 and cyclazocine). Metaphit did not affect pentobarbital-induced loss of righting, head-drop and eye closure. Metaphit itself induced a PCP-like catalepsy. Isobolographic analysis of the interactions between metaphit and PCP-like drugs suggested that metaphit potentiated the catalepsy-inducing effects of these drugs. The possibility that metaphit exerts its potentiating effects by inhibition of PCP biotransformation was evaluated by measuring plasma and brain concentrations of PCP after pretreatment with either metaphit or SKF-525A, an inhibitor of the enzyme systems involved in PCP biotransformation. SKF-525A, but not metaphit, increased brain levels of PCP. The results suggest that metaphit acts not as an antagonist of PCP but as a less-potent, long-acting, specific PCP-like agonist. Potentiation by metaphit of the cataleptic effects of chemically diverse drugs with PCP-like actions does not appear to be based on inhibition of the enzyme systems involved in metabolism of those drugs.

Acylation↗
PubMed1984

Phencyclidine-induced catalepsy in pigeons: specificity and stereoselectivity.

A procedure is described for the rapid assessment of cataleptic activity (loss of righting, without head-drop and without eye closure) of phencyclidine-type drugs. Single- and cumulative-dosing procedures with phencyclidine and ketamine produced similar results. Pentobarbital produced loss of righting at doses which also induced head-drop and eye closure. Catalepsy was induced exclusively by the d-isomers of ketamine, 1-(1-phenylcyclohexyl)-3-methylpiperidine and alpha-dioxadrol. The procedure is suitable for studying compounds which may interact with phencyclidine receptors.

Animals↗
PubMed1984

3-[18F]Acetylcyclofoxy: a useful probe for the visualization of opiate receptors in living animals.

A fluoro-analogue of the potent narcotic antagonist, naltrexone, was synthesized and shown to bind with high affinity to opiate receptors in vitro. 3-[18F]acetylcyclofoxy was prepared via a one-step triflate displacement reaction with the positron emitting 18F ion from tetraethylammonium [18F] fluoride. 3-[18F]acetylcyclofoxy accumulation in opiate receptor rich brain regions of both rat and baboon is shown to be completely displaced by the active enantiomer of naloxone [-)-naloxone) while the identical dose of the pharmacologically inert (+)-naloxone has no detectable effect. Moreover, both rat and baboon brain showed the well documented, typical opiate receptor distribution so that basal ganglia and thalamus are clearly visible in the living baboon brain up to 95 min after intravenous injection of 3-[18F] acetylcyclofoxy. We expect that 3-[18F )acetylcyclofoxy will be a useful probe for visualizing opiate receptors in living humans.

Animals↗
PubMed1984

Tritiated-6-beta-fluoro-6-desoxy-oxymorphone: a highly selective ligand for the opiate mu receptor whose binding is characterized by low nonspecific binding.

In this paper we examine the binding of [3H]FOXY (tritiated-6-beta-fluoro-6-desoxy-oxymorphone) to membranes of rat brain. Using the site-directed alkylating agents BIT and FIT, evidence is presented that [3H]FOXY selectively labels mu opiate binding sites in vitro. Further, BIT and FIT did not significantly affect [3H]bremazocine binding to kappa receptors. Scatchard plots of [3H]FOXY binding were somewhat curvilinear, suggesting the presence of two classes of mu binding sites. At concentrations up to 19 nM, 90 percent of the total binding was specific. The combination of high mu-selectivity and low nonspecific binding suggests the [3H]FOXY may prove to be a powerful tool for studying the opiate mu receptor.

Animals↗
PubMed1984

Probes for narcotic receptor mediated phenomena. 10. Irreversible ligands to opioid receptors based on biologically potent endoethenooripavines. Reversible binding of fit to mu and delta opioid receptors.

A p-isothiocyanatophenylacetylamino moiety at the C7alpha position on an endoethenooripavine (NIH 10358) was found to irreversibly bind to both the mu and delta opioid receptors in rat brain membrane preparations. However, the same endoethenooripavine nucleus with a p-methylfumaroylaminophenylacetylamino moiety at that position (NIH 10364) binds specifically and irreversibly to only mu opioid receptors. Hypotheses are being developed concerning receptor subclass alkylation specificity. For example, it has now been found that the delta receptor irreversible agonist, FIT, can interact with both mu and delta receptors in a reversible manner.

Alkylating Agents↗
PubMed1984

Preparation of rat brain membranes greatly enriched with either type-I-delta or type-II-delta opiate binding sites using site directed alkylating agents: evidence for a two-site allosteric model.

Although it is widely accepted that radiolabeled prototypic delta receptor agonists label two binding sites in vitro, the mechanism by which mu ligands inhibit peptide binding as well as the identity of the binding sites remains unsettled (Rothman and Westfall, Mol. Pharmacol. 21:538-547, 1982 ; Bowen et al., Proc. Natl. Acad. Sci. U.S.A. 78:4818-4822, 1981). Using the site directed, receptor selective alkylating agents, BIT and FIT (Rice et al., Science 220:314-316, 1983), we describe the preparation of membranes devoid of high affinity binding sites and demonstrate that the mu agonist oxymorphone noncompetitively inhibits the binding of [3H]DADL to the residual lower affinity binding sites.

Alkylating Agents↗