A desensitization-selective potentiator of AMPA-type glutamate receptors. (57/267)

1: We examined the effects of PEPA, an allosteric potentiator of AMPA receptors, on AMPA receptor kinetics. 2: PEPA did not affect the deactivation of glutamate responses but potently attenuated the extent of receptor desensitization without slowing the onset of desensitization in most of the recombinant AMPA receptors (GluR1-flip, GluR1-flop, GluR3-flip, GluR3-flip+GluR2-flip, and GluR3-flop+GluR2-flop) expressed in Xenopus oocytes. For the GluR3-flop subunit, PEPA attenuated the extent of desensitization and only weakly prolonged deactivation (1.3 fold). 3: PEPA did not significantly affect recovery from desensitization in oocytes expressing GluR3-flip, GluR1-flop, and GluR1-flop, but weakly accelerated (2.6 fold) recovery from desensitization in oocytes expressing GluR3-flop. 4: PEPA's effect on desensitization of GluR3-flop-containing receptors is unique in that onset is very slow. 5: Simulation studies using simplified kinetic models for AMPA receptors are utilized to explore the differential effects of PEPA on GluR3-flip and -flop. It is possible to simulate the action on GluR3-flip by modulating two rate constants in a 12-state kinetic model. For simulation of the action on GluR3-flop, the 12-state kinetic model is not enough, and it is necessary to invoke a 13th state, a PEPA-bound receptor to which glutamate cannot bind. 6: These results suggest that attenuation of extent of desensitization represents the principal mechanism underlying the potentiation of AMPA receptors by PEPA, and that PEPA exhibits different mechanisms with respect to GluR3-flip and GluR3-flop.  (+info)

Attenuated renal excretion in response to thiazide diuretics in Gitelman's syndrome: a case report. (58/267)

Gitelman's syndrome is a variant of Bartter's syndrome characterized by hypocalciuria and hypomagnesemia. The administration of thiazide diuretics may induce a subnormal increase of urinary Na+ and Cl- excretion in patients with Gitelman's syndrome, consistent with the hypothesis that less Na+ and Cl- than normal is reabsorbed by the thiazide-inhibitable transporter in Gitelman's syndrome. Specific mutations of NaCl cotransporter, coupled with mutant NaCl cotransporter expression studies clearly demonstrated that many of the characteristics of individuals with Gitelman's syndrome are explained by lack of function of NaCl cotransporter. We recently diagnosed a patient with Gitelman's syndrome by performing the thiazide and furosemide tests, and it is suggested that the clearance studies by diuretic administration may be of diagnostic help in Gitelman's syndrome.  (+info)

Effects of 5'-alkyl-benzothiadiazides on (R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor biophysics and synaptic responses. (59/267)

Alkyl-substituted benzothiadiazides (BTDs) were tested for their effects on (R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors. In excised patches, the 5'-ethyl derivative "D1" blocked the desensitization of AMPA receptor currents during prolonged application of glutamate (EC(50), 36 microM), and it slowed deactivation of responses elicited by 1-ms glutamate pulses greater than 10-fold. [(3)H]Fluorowillardiine binding to rat synaptic membranes was increased by D1 by a factor of 3.6 (EC(50), 17 microM) with a Hill coefficient near 2. In hippocampal slices, the compound reversibly increased excitatory postsynaptic currents and field excitatory postsynaptic potentials (EPSPs) with thresholds around 10 microM. The size of the alkyl substituent influenced both the potency and nature of the drug effect on synaptic currents: 5'-methyl compounds had a 2-fold greater effect on response amplitude than on response duration, whereas 5'-ethyl compounds like D1 caused greater increases in duration than amplitude. In tests with recombinantly expressed AMPA receptor subunits, D1 preferred the glutamate receptor (GluR) subunit GluR4 flip (0.64 microM) over GluR4 flop (5.3 microM); similar affinities but with smaller flip-flop differences were obtained for GluR1 through 3. These results show that D1 and congeners are significantly more potent than the parent compound IDRA-21 and that they differ in two fundamental aspects from cyclothiazide, the most widely studied BTD: 1) D1 markedly increases the agonist affinity of AMPA receptors and 2) it has immediate and large effects on field EPSPs. The large gain in potency conferred by alkyl substitution suggests that the 5' substituent is in intimate contact with the receptor, with the size of the substituent determining the way in which receptor kinetics is changed.  (+info)

Serum uric acid in hypertensive patients. (60/267)

Both the average serum uric acid and annual increment were determined in 250 treated patients attending a hypertension clinic. The average serum uric acid was greater in men compared with women, in patients receiving a thiazide diuretic and in patients with a high average plasma urea. The mean annual increment in uric acid was close to zero (0.0017 mmol/litre per year) and was not related to sex, age, blood pressure control, diuretic therapy, or plasma urea. There was an unexplained positive association between annual increment and methyldopa therapy though this drug was not associated with a significantly high average serum uric acid. A table is presented giving the theoretical upper limits for average serum uric acid according to sex, plasma urea concentration, and whether or not a thiazide diuretic has been prescribed. It is hoped that this table will be of assistance in assessing the normality or otherwise of a high serum uric acid found in a hypertensive patient.  (+info)

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels lacking the N-terminal domain. (61/267)

Ionotropic glutamate receptor (iGluR) subunits contain a approximately 400-residue extracellular N-terminal domain ("X domain"), which is sequence-related to bacterial amino acid-binding proteins and to class C G-protein-coupled receptors. The X domain has been implicated in the assembly, transport to the cell surface, allosteric ligand binding, and desensitization in various members of the iGluR family, but its actual role in these events is poorly characterized. We have studied the properties of homomeric alpha-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA)-selective GluR-D glutamate receptors carrying N-terminal deletions. Our analysis indicates that, surprisingly, transport to the cell surface, ligand binding properties, agonist-triggered channel activation, rapid desensitization, and allosteric potentiation by cyclothiazide can occur normally in the complete absence of the X domain (residues 22-402). The relatively intact ligand-gated channel function of a homomeric AMPA receptor in the absence of the X domain indirectly suggests more subtle roles for this domain in AMPA receptors, e.g. in the assembly of heteromeric receptors and in synaptic protein interactions.  (+info)

Rational Prescribing in Primary Care (RaPP-trial). A randomised trial of a tailored intervention to improve prescribing of antihypertensive and cholesterol-lowering drugs in general practice [ISRCTN48751230]. (62/267)

BACKGROUND: The underlying reasons for differences between clinical practice and systematically developed guidelines vary from one clinical problem to another. It is therefore logical to tailor strategies to support the implementation of guidelines to address identified barriers to change. The objective of this trial is to evaluate the effects of a tailored intervention to support the implementation of systematically developed guidelines for the use of antihypertensive and cholesterol-lowering drugs for the primary prevention of cardiovascular disease. METHODS/DESIGN: Unblinded, cluster-randomised trial. 150 general practices will be recruited from two geographical areas in Norway, and randomised to the intervention or control group (passive dissemination of guidelines). Outcomes will be measured for all eligible patients seen in the participating practices during one year after the intervention. A multifaceted intervention has been tailored to address identified barriers to change. Key components are an educational outreach visit with audit and feedback, and computerised reminders. Pharmacists will conduct the visits. During the outreach visit the main recommendations will be presented and software will be installed that links to the electronic medical record systems used in the participating practices. The software will perform an audit that will be fed back during the visit, present pop-up reminders for patients with high blood pressure or cholesterol, and provide a cardiovascular risk calculator and patient education material. The main outcomes are the proportions of 1) first time prescriptions for hypertension where thiazides are not prescribed, 2) patients not assessed for cardiovascular risk before prescribing antihypertensive or cholesterol-lowering drugs, and 3) patients treated for hypertension or high cholesterol for three months or more who have not achieved recommended treatment goals.  (+info)

Ultrastructural contributions to desensitization at cerebellar mossy fiber to granule cell synapses. (63/267)

Postsynaptic AMPA receptor desensitization leads to depression at some synapses. Here we examine whether desensitization occurs at mossy fiber to granule cell synapses and how synaptic architecture could contribute. We made whole-cell voltage-clamp recordings from granule cells in rat cerebellar slices at 34 degrees C, and stimulated mossy fibers with paired pulses. The amplitude of the second EPSC was depressed by 60% at 10 msec and recovered with tau approximately 30 msec. This fast component of recovery from depression was reduced by cyclothiazide and enhanced when release probability was increased, suggesting that it reflects postsynaptic receptor desensitization. We evaluated the importance of synaptic ultrastructure to spillover and desensitization by using serial electron microscopy to reconstruct mossy fiber glomeruli. We found that mossy fiber boutons had hundreds of release sites, that the average center-to-center distance between nearest release sites was 0.46 microm, and that these sites had an average of 7.1 neighbors within 1 microm. In addition, glia did not isolate release sites from each other. By contrast, desensitization plays no role in paired-pulse depression at the cerebellar climbing fiber, where glial ensheathment of synapses is nearly complete. This suggests that the architecture of the mossy fiber glomerulus can lead to desensitization and short-term depression. Modeling indicates that, as a consequence of the close spacing of release sites, glutamate released from a single site can desensitize AMPA receptors at neighboring sites, even when the probability of release (p(r)) is low. When p(r) is high, desensitization would be accentuated by such factors as glutamate pooling.  (+info)

Fatal acute poisoning by bentazon. (64/267)

A case of fatal suicidal bentazon poisoning is presented along with a description of the different analytical methods involved. A 56-year-old farmer was examined by the family doctor 1 h after voluntarily ingesting 500 mL of FIGHTER (bentazon, 480 g/L water). He presented a Glasgow score of 15, polypnea, diarrhea, and vomiting. During transport by ambulance to the hospital, he tossed, sweated, and suddenly presented breathing difficulty followed by heart failure. Tracheal intubation was impossible (H1.5) despite use of different diameter cannulas because of extreme general muscle rigidity. All attempts at resuscitation failed, and the patient died within 2 h postingestion. Blood and urine samples were taken just before death. General basic and neutral drug screening by high-performance liquid chromatography-diode-array detection and gas chromatography-nitrogen-phosphorus detection showed no strychnine or other drugs or toxics except for citalopram (< 0.1 mg/L) and bentazon, but this weak acidic molecule (pKa3.3) was badly extracted in alkaline conditions. Plasma and urine levels, measured after acidic extraction, protein precipitation, or simple dilution, were 1500 and 1000 mg/L, respectively. Bentazon (M.W. 240) was confirmed by its basic mass spectrum (ESI-, m/z 239, 197, 175, 132) or by that of methylated derivative (El+, m/z 254, 212, 175). An hydroxylated metabolite (ESI-, m/z 255, 213, 191, 148; El+, m/z 284, 242, 163) and the N1-glucuronide conjugate of bentazon (ESI-, m/z 415, 239) were also detected in urine. (Quantitation ions are underlined.) This first case of bentazon poisoning with available analytical data revealed the high toxicity of this compound after large dose ingestion with early and heavy symptoms such as muscle rigidity probably related to muscular toxicity. Comparison with another nonfatal case and with toxicological data on animals is discussed.  (+info)