Guide to receptors and channels, 2nd edition.
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Humans↗
Biomedical subjects
J A Peters
Publications and source records attributed to J A Peters.
Novel structural determinants of single-channel conductance in nicotinic acetylcholine and 5-hydroxytryptamine type-3 receptors.
Nicotinic ACh (acetylcholine) and 5-HT3 (5-hydroxytryptamine type-3) receptors are cation-selective ion channels of the Cys-loop transmitter-gated ion channel superfamily. Numerous lines of evidence indicate that the channel lining domain of such receptors is formed by the alpha-helical M2 domain (second transmembrane domain) contributed by each of five subunits present within the receptor complex. Specific amino acid residues within the M2 domain have accordingly been demonstrated to influence both single-channel conductance (gamma) and ion selectivity. However, it is now clear from work performed on the homomeric 5-HT3A receptor, heteromeric 5-HT3A/5-HT3B receptor and 5-HT3A/5-HT3B receptor subunit chimaeric constructs that an additional major determinant of gamma resides within a cytoplasmic domain of the receptor termed the MA-stretch (membrane-associated stretch). The MA-stretch, within the M3-M4 loop, is not traditionally thought to be implicated in ion permeation and selection. Here, we describe how such observations extend to a representative neuronal nicotinic ACh receptor composed of alpha4 and beta2 subunits and, by inference, probably other members of the Cys-loop family. In addition, we will attempt to interpret our results within the context of a recently developed atomic scale model of the nicotinic ACh receptor of Torpedo marmorata (marbled electric ray).
Amino Acid Sequence↗
Histochemistry defines a proteoglycan-rich layer in bovine flexor tendon subjected to bending.
Mid-substance fibrocartilage develops in bovine deep flexor tendon at the point where the tendon wraps under sesamoid bones of the foot and receives transverse compressive loading during locomotion. Fibrocartilage extends several millimeters into the tendon at this location and the proteoglycan-rich tissue stains intensely with Alcian blue. Using histochemical techniques we demonstrate the presence of aggrecan, type VI collagen, and hyaluronic acid in the extracellular matrix of this region of tendon. Biglycan staining was localized to the cells, however. Adjacent to the fibrocartilage, at the outer curvature of the tendon as it bends, the tissue resembles typical tensile tendon with dense bundles of linearly arranged collagen. Longitudinal sections revealed discrete layers of Alcian blue-stained material between the collagen bundles. We demonstrate that these layers of loose matrix also contain aggrecan, type VI collagen, and hyaluronic acid. However, the dense collagen bundles of this region are negative for these components. Transverse sections of tendon in the area adjacent to fibrocartilage show a distinct Alcian blue-stained structure surrounding vascular elements at the point where several fiber bundles come together. This is concluded to be the same structure as the Alcian blue-stained layers seen in longitudinal sections. These observations suggest that proteoglycan-rich matrices in tendon subjected to mechanical loading other than pure tension may serve multiple roles. Such matrices can not only provide compressive stiffness and separate and lubricate collagen bundles that move relative to each other, but may also protect the integrity of vasculature in tendon subjected to bending and shear.
Aggrecans↗
The interaction of anaesthetic steroids with recombinant glycine and GABAA receptors.
BACKGROUND: Anaesthetic steroids are established positive allosteric modulators of GABAA receptors, but little is known concerning steroid modulation of strychnine-sensitive glycine receptors, the principal mediators of fast, inhibitory neurotransmission in the brain stem and spinal cord. This study compared the modulatory actions of five anaesthetic pregnane steroids and two non-anaesthetic isomers at human recombinant alpha1 glycine and alpha1beta2gamma2L GABAA receptors. METHODS: Recombinant alpha1 glycine or alpha1beta2gamma2L GABAA receptors were expressed in Xenopus laevis oocytes and agonist-evoked currents recorded under voltage-clamp. Steroid modulation of currents evoked by GABA, or glycine, was quantified by determining the potency (EC50) and maximal effect of the compounds. RESULTS: The anaesthetics minaxolone (EC50=1.3 microM), Org20599 (EC50=1.1 microM) and alphaxalone (EC50=2.2 microM) enhanced currents mediated by GABAA receptors. The anaesthetics also enhanced currents mediated by glycine receptors, although with higher EC50 values (minaxolone 13.1 microM; Org20599=22.9 microM and alphaxalone=27.8 microM). The maximal enhancement (to 780-950% of control) produced by the three steroids acting at the GABAA receptor was similar, but currents evoked by glycine were potentiated with increasing effectiveness by alphaxalone (199%) <Org20599 (525%) <minaxolone (1197%). The anaesthetic isomers, 5alpha-pregnan-3alpha-ol-20-one and 5beta-pregnan-3alpha-ol-20-one (eltanolone) enhanced GABAA receptor-mediated currents with similar potency and efficacy, but only the former enhanced glycine, the latter causing inhibition. The non-anaesthetic steroids 5alpha-pregnan-3beta-ol-20-one and 5beta-pregnan-3beta-ol-20-one modulated neither GABAA, nor glycine, receptors. CONCLUSIONS: The data demonstrate that structure-activity relationships for steroid modulation at glycine and GABAA receptors differ. Comparing the EC50 values reported here with free plasma concentrations during steroid-induced anaesthesia indicates that a selective modulation of GABAA receptor activity is likely to occur in vivo.
Anesthetics↗
Guide to receptors and channels, 1st edition.
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Ion Channels↗
The 5-hydroxytryptamine type 3 (5-HT3) receptor reveals a novel determinant of single-channel conductance.
5-HT3 (5-hydroxytryptamine type 3) receptors are cation-selective ion channels of the Cys-loop transmitter-gated ion channel superfamily. Two 5-HT3 receptor subunits, 5-HT3A and 5-HT3B, have been characterized in detail, although additional putative 5-HT3 subunit genes (HTR3C, HTR3D and HTR3E) have recently been reported. 5-HT3 receptors function as homopentameric assemblies of the 5-HT3 subunit, or heteropentamers of 5-HT3A and 5-HT3B subunits of unknown stoichiometry. The single-channel conductances of human recombinant homomeric and heteromeric 5-HT3 receptors are markedly different, being <1 and approx. 16 pS respectively. Paradoxically, from the results of studies performed on the closely related nicotinic acetylcholine receptor, the channel-lining M2 domain of the 5-HT3A subunit is predicted to enhance cation conduction, whereas that of the 5-HT3B subunit would not. The present study describes a novel determinant of single-channel conductance, out with the M2 domain, which accounts for this anomaly. Utilizing a panel of chimaeric 5-HT3A and 5-HT3B subunits, a profound determinant of single-channel conductance was traced to a putative amphipathic helix (the 'HA stretch') within the large cytoplasmic loop of the receptor. Replacement of three arginine residues (R432, R436 and R440) unique to the HA stretch of the 5-HT3A subunit with the aligned residues (Q395, D399 and A403) of the 5-HT3B subunit increased the single-channel conductance 28-fold. Significantly, from ultrastructural studies of the Torpedo nicotinic acetylcholine receptor, the key residues may be components of narrow openings within the inner vestibule of the channel, located in the cytoplasm, which contribute to the permeation pathway. Our findings indicate an important and hitherto unappreciated function for the HA stretch in the Cys-loop family of transmitter-gated ion channels.
Amino Acid Sequence↗
GABAA receptor modulation by the novel intravenous general anaesthetic E-6375.
E-6375 (4-butoxy-2-[4-(2-cyanobenzoyl)-1-piperazinyl] pyrimidine hydrochloride) is a new intravenous general anaesthetic with an anaesthetic potency, in mice, comparable to propofol, or etomidate. Here, we examined the effect of E-6375 upon the GABAA receptor, a putative target of intravenous anaesthetic action. E-6375 reversibly enhanced GABA-evoked currents mediated by recombinant GABAA (alpha1beta2gamma2L) receptors expressed in Xenopus laevis oocytes, with little effect on NMDA- and kainate-evoked currents mediated by NR1a/NR2A and GluR1o/GluR2o glutamate receptors, respectively. E-6375 prolonged the decay of GABA-evoked miniature inhibitory postsynaptic currents recorded from rat Purkinje neurones demonstrating the anaesthetic also enhanced the activity of synaptic GABAA receptors. The GABA enhancing action of E-6375 on recombinant GABAA receptors was unaffected by the subtype of the alpha isoform (i.e. alphaxbeta2gamma2L; x=1-3) within the receptor, but was increased by the omission of the gamma2L subunit. Receptors incorporating beta2, or beta3, subunits were more sensitive to modulation by E-6375 than those containing the beta1 subunit. The selectivity of E-6375 was largely governed by the identity (serine or asparagine) of a single amino acid residue within the second transmembrane domain of the beta-subunit. The various in vivo actions of general anaesthetics may be mediated by GABAA receptor isoforms that have a differential distribution within the CNS. The identification of agents, such as E-6375, that discriminate between GABAA receptor subtypes may augur the development of general anaesthetics with an improved therapeutic profile.
Amino Acid Sequence↗
[Rupture of thoracic aneurysm in a 10-year old boy].
A 10-year-old boy with a medical history of fatigue became nauseous, short of breath and cyanotic within 24 hours after a frightening incident. He was successfully resuscitated after a cardiac arrest. A CT scan revealed a ruptured aneurysm of the ascending aorta. During emergency surgery the ascending aorta and aortic arch were replaced with a 22 mm synthetic graft. No postoperative complications occurred. There was no associated trauma, syphilis, collagen diseases (Marfan's syndrome, Ehlers-Danlos syndrome), congenital heart disease or autoimmune disease. The cause of the aneurysm and rupture remain unclear.
Aorta, Thoracic↗
Alpha-amino acid phenolic ester derivatives: novel water-soluble general anesthetic agents which allosterically modulate GABA(A) receptors.
In the search for a novel water-soluble general anesthetic agent the activity of an alpha-amino acid phenolic ester lead, identified from patent literature, was markedly improved. In addition to improving in vivo activity in mice, good in vitro activity at GABA(A) receptors was also conferred. Within the series of compounds good enantioselectivity for both in vitro and in vivo activity was found, supporting a protein-mediated mechanism of action for anesthesia involving allosteric modulation of GABA(A) receptors. alpha-Amino acid phenolic ester 19, as the hydrobromide salt Org 25435, was selected for clinical evaluation since it retained the best overall anesthetic profile coupled with improved stability and water solubility. In the clinic it proved to be an effective intravenous anesthetic in man with rapid onset of and recovery from anesthesia at doses of 3 and 4 mg/kg.
Allosteric Regulation↗
Relaxivity and water exchange studies of a cationic macrocyclic gadolinium(III) complex.
We conducted relaxometric and water exchange studies of the cationic [Gd((S,S,S,S)-THP)(H2O)]3+ complex (THP 1,4,7,10-tetrakis(2-hydroxy-propyl)-1,4,7,10-tetraazacyclododecane). While the NMRD profiles obtained are typical for DOTA-like complexes (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), variable-temperature 7O NMR investigations revealed a relatively high water exchange rate (k(298)(ex) = 1.89 x 10(7) s(-1)). These results differ from those reported for other cationic tetraamide macrocyclic Gd(III) complexes, which exhibit characteristically low exchange rates. Since the low exchange rates are attributed partially to the geometry of the M isomer (square antiprismatic) in the tetraamide derivatives, the atypical water exchange rate observed in [Gd((S,S,S,S)-THP-(H2O)]3+ may result from a twisted square antiprismatic structure in this complex and from the relatively high steric strain at the water coordination site as a result of the presence of methyl groups at the alpha-position with respect to the Gd(III)-bound O atoms of THP.
Journal Article↗
One-step synthesis of a highly active, mesoporous, titanium-containing silica by using bifunctional templating.
A highly active, three-dimensional, mesoporous titanosilica, TiTUD-1, with comparable properties to Ti-grafted mesoporous silica MCM-41, has been prepared in a one-step synthesis. A non-surfactant chemical, triethanolamine, was used as a template molecule. Triethanolamine easily forms complexes with titanium alkoxides, yielding titanatrane complexes, which together with free triethanolamine form meso-sized aggregates that template mesopores upon increasing the temperature of the synthesis mixture. Triethanolamine served as both mesopore template and ligand for the titanium complexes, which represent the majority of the catalytic-site precursors. The formation of the silica network and the titanium insertion were followed by a combination of diffuse reflectance UV/ Vis/NIR and FTIR spectroscopy. A titanium-rich phase was obtained on the mesopore surfaces during calcination, allowing for easy accessibility of the reactants to the catalytic sites. TiTUD-1 is about six times more active than framework-substituted Ti-MCM-41 and has similar activity to Ti-grafted MCM-41.
Journal Article↗
The combined hydrolysis and hydrogenation of inulin catalyzed by bifunctional Ru/C.
A one-pot process for hydrolysis and hydrogenation of inulin to D-mannitol and D-glucitol over a bifunctional Ru/C catalyst was developed. The hydrolysis is catalyzed by the carbon support, onto which acidity was introduced by pre-oxidation. The effect of different carbon treatments on the hydrolysis of inulin was studied. Oxidation with ammonium peroxydisulfate resulted in a carbon with the highest hydrolysis activity. On this carbon, long chain inulin is hydrolyzed faster than inulin rich in short chains. The application of high pressure (up to 100 bar) increased the hydrolysis rate substantially. The combined process was successfully conducted with a Ru-catalyst supported on this oxidized carbon.
Carbohydrate Conformation↗
Zirconium(IV) complexes of oxydiacetic acid in aqueous solution and in the solid state as studied by multinuclear NMR and X-ray crystallography.
The structures of complexes of Zr(IV) and oxydiacetate (ODA2-) in aqueous solutions of pH 0-7 were investigated with the use of 1H, 13C, and 17O NMR spectroscopy. Equilibria of mononuclear [Zr(oda)]2+, [Zr(oda)2], and [Zr(oda)3]2- complexes have been observed. In all complexes ODA2- is bound in a tridentate fashion through the two carboxylate groups and the ether oxygen. No di- or oligonuclear species containing ODA2- were observed. An excess of free Zr(IV) remains in solution, probably as a result of weak electrostatic interactions between negatively charged Zr-ODA complexes or free ODA2- and a positively charged cyclic tetranuclear hydroxy zirconium complex. CP-MAS 13C NMR spectra of solid compounds isolated from the samples indicated that the structures of the [Zr(oda)2] and [Zr(oda)3]2- complexes in solution are similar to those in the solid state. This is corroborated by the single-crystal X-ray structure of Na2[Zr(oda)3] x 5.5 H2O, which was obtained from a solution containing exclusively the [Zr(oda)3]2- complex. In this structure Zr(IV) is nine-coordinate with the three ODA2- ligands bound in a tricapped trigonal prismatic geometry. The negative charge of this [Zr(oda)3]2complex is balanced by two Na+ ions, one of which is on a center of symmetry between delta and lambda enantiomers of [Zr(oda)3]2-. This Na+ is octahedrally coordinated to six (non Zr(IV)-bound) carboxylate oxygen atoms of six different [Zr(oda)3]2- units.
Journal Article↗
Inulin as a carrier for contrast agents in magnetic resonance imaging.
Magnetic resonance angiography (MRA) has put forth an impetus for the development of macromolecular GdIII complexes that have a prolonged lifetime in the vascular system. Herein, we report the synthesis and GdIII complexation of a new sugar conjugate based on inulin and the DO3A ligand (DO3A = 1,4,7,10-tetraazacyclododecan-1,4,7-triacetic acid). Two API-DO3ASQ conjugates (API = O-(aminopropyl)inulin, SQ = squaric acid = 3,4-dihydroxy-3-cyclobutene-1,2-dione) with different degrees of substitution (ds = 0.7 and ds = 1.5) were prepared from API by using the diethyl ester of squaric acid as a linking agent for the DO3A chelate. The efficacies of the resulting GdIII compounds were evaluated by investigation of their water 1H longitudinal-relaxation-rate enhancements at variable field (NMRD). A dramatic increase in relaxivity was observed in the more highly substituted conjugate (ds = 1.5); this prompted us to do a variable-temperature (17)O study in order to further characterize the relaxation parameters involved in this system. [Gd(API-DO3ASQ)] shows promising properties for application as a contrast agent for MRI.
Chelating Agents↗
Neurosteroid modulation of recombinant and synaptic GABAA receptors.
Certain pregnane steroids are now established as potent, positive allosteric modulators of the gamma-aminobutyric acid type A (GABAA) receptor. These compounds are known to be synthesized in the periphery by endocrine glands, such as the ovaries and the adrenal glands, and can rapidly cross the blood-brain barrier. Therefore, such steroids could act as endogeneous modulators of the major inhibitory receptor in the mammalian central nervous system. However, the demonstration that certain neurons and glia can synthesize the pregnane steroids (i.e., neurosteroids) additionally suggests that they may serve a paracrine role by influencing GABAA-receptor function through their local release in the brain itself. Here, we demonstrate that these neurosteroids are highly selective and extremely potent modulators of the GABAA receptor. The subunit composition of the GABAA receptor may influence the actions of the neurosteroids, particularly when considering concentrations of these agents thought to occur physiologically, which may underlie their reported differential effects at certain inhibitory synapses. However, recent work suggests that the phosphorylation status of either the synaptic GABAA receptor or its associated proteins may also influence neurosteroid sensitivity; these findings are discussed. Upon administration, the neurosteroids exhibit clear behavioral effects, including sedation, anticonvulsant actions, and behaviors predictive of anxiolysis; when given at high doses, they induce general anesthesia. Numerous synthetic steroids have been synthesized in an attempt to therapeutically exploit these properties, and these data are reviewed in this chapter. However, targeting the brain enzymes that synthesize and metabolize the neurosteroids may offer a new approach to exploit this novel endocrine-paracrine neurotransmitter interaction.
Animals↗
Modulation of native and recombinant GABA(A) receptors by endogenous and synthetic neuroactive steroids.
Upon administration, certain pregnane steroids produce clear behavioural effects including, anxiolysis, sedation, analgesia, anaesthesia and are anti-convulsant. This behavioural profile is characteristic of compounds that act to enhance the actions of GABA acting at the GABA(A) receptor. In agreement, numerous studies have now demonstrated these steroids to be potent, positive allosteric modulators of the GABA(A) receptor. The pregnane steroids are synthesized in the periphery by endocrine glands such as the adrenals and the ovaries, but are also made by neurons and glial cells in the central nervous system itself. Hence, these compounds could play both an endocrine and a paracrine role to influence neuronal excitability by promoting inhibition. Here we review evidence that the pregnane steroids are highly selective and extremely potent GABA(A) receptor modulators and that their effects at 'physiological' concentrations (low nanomolar) may be influenced by the subunit composition of the GABA(A) receptor. This feature may underlie recent findings demonstrating the effects of the neurosteroids on inhibitory synaptic transmission to be brain region dependent, although recent reports suggest that phosphorylation mechanisms may additionally influence neurosteroid sensitivity of the GABA(A) receptor. Numerous synthetic steroids have been synthesized in an attempt to therapeutically exploit the behavioural effects of the pregnane steroids and progress with this approach will be discussed. However, the demonstration that the steroids may be made within the central nervous system offers the alternative strategy of targeting the enzymes that synthesize/metabolise the neurosteroids to exploit this novel endocrine/paracrine interaction.
Animals↗
Proportion of heritable paraganglioma cases and associated clinical characteristics.
OBJECTIVE/HYPOTHESIS: To determine the heritable proportion of paraganglioma (PGL) and identify clinical features associated with heritable PGL. STUDY DESIGN: Patients diagnosed with head and neck PGLs, identified retrospectively through clinical otolaryngology practices and/or participation in previous PGL research studies, were given a medical and family history questionnaire. METHODS: Questionnaire information was used to classify participants as having "heritable" or "non-heritable" cases of PGL. Classification of the participants identified through otolaryngology clinics was used to estimate the heritable proportion of PGL. Statistical analysis was performed to identify significant differences in the clinical characteristics of the heritable versus non-heritable groups. RESULTS: Among the otolaryngology clinic population, 35% were classified as having heritable PGL. Individuals with heritable PGL were younger on average than those with non-heritable PGL. The majority of non-heritable participants were female, but there was an equal gender ratio among the heritable participants. Individuals diagnosed with a carotid body tumor (CBT) were 5.8 times more likely to be classified as heritable than those diagnosed with PGL at other anatomic locations. CONCLUSIONS: Approximately 35% of individuals who present to an otolaryngologist with a head and neck PGL have inherited a predisposition for this growth. Among individuals diagnosed with head and neck PGL, those diagnosed with CBT are 5.8 times more likely to have an inherited predisposition than those diagnosed with PGL at other anatomic locations.
Adult↗
Motivations and concerns of patients with access to genetic testing for hereditary pancreatitis.
OBJECTIVES: Direct DNA testing is now available for hereditary pancreatitis (HP). This study aimed to identify the factors that motivated individuals to participate in research and to determine how research participants used their genetic test results. METHODS: A survey was mailed to 247 participants (110 male, 137 female) who were > or =18 yr of age and living in the US. Data analysis was primarily a description of frequency distribution of the responses. RESULTS: Ninety-one of 247 participants (37%) completed the survey. Of the 55 female and 36 male respondents, 60% were 31-55 yr old, and a total of 54% tested positive for HP. The most common reason for participating in research was "to help a relative/family member" (61%), and genetic testing was pursued because of "the disturbance of seeing affected relatives" (48%) and "the desire to help future generations" (33%). Perceived risk of developing HP in the future was the least important motivating factor in seeking genetic testing. Sixty-two percent of respondents had received their genetic test results. All but one chose to share their results with at least one person: most often with family members (96%) and physicians (62%), and least often with insurance companies (4%). The most common influential factor in withholding information was "the fear of insurance discrimination" (23%). CONCLUSIONS: The major motivations to participate in the HP genetic research study were to obtain genetic testing and to help current family members and future generations. The major concern was insurance discrimination. Participants clearly appreciate the availability of genetic testing for HP. These results suggest that a mechanism to disclose results to research participants should be considered, and effective ways to protect at-risk individuals from insurance discrimination must remain a genetics health care priority.
Adult↗