Magnesium gates glutamate-activated channels in mouse central neurones
TL;DR: The voltage dependence of the NMDA receptor-linked conductance appears to be a consequence of the voltage dependenceof the Mg2+ block and its interpretation does not require the implication of an intramembrane voltage-dependent ‘gate’.
Abstract: The responses of vertebrate neurones to glutamate involve at least three receptor types. One of these, the NMDA receptor (so called because of its specific activation by N-methyl-D-aspartate), induces responses presenting a peculiar voltage sensitivity. Above resting potential, the current induced by a given dose of glutamate (or NMDA) increases when the cell is depolarized. This is contrary to what is observed at classical excitatory synapses, and recalls the properties of 'regenerative' systems like the Na+ conductance of the action potential. Indeed, recent studies of L-glutamate, L-aspartate and NMDA-induced currents have indicated that the current-voltage (I-V) relationship can show a region of 'negative conductance' and that the application of these agonists can lead to a regenerative depolarization. Furthermore, the NMDA response is greatly potentiated by reducing the extracellular Mg2+ concentration [( Mg2+]o) below the physiological level (approximately 1 mM). By analysing the responses of mouse central neurones to glutamate using the patch-clamp technique, we have now found a link between voltage sensitivity and Mg2+ sensitivity. In Mg2+-free solutions, L-glutamate, L-aspartate and NMDA open cation channels, the properties of which are voltage independent. In the presence of Mg2+, the single-channel currents measured at resting potential are chopped in bursts and the probability of opening of the channels is reduced. Both effects increase steeply with hyperpolarization, thereby accounting for the negative slope of the I-V relationship of the glutamate response. Thus, the voltage dependence of the NMDA receptor-linked conductance appears to be a consequence of the voltage dependence of the Mg2+ block and its interpretation does not require the implication of an intramembrane voltage-dependent 'gate'.
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TL;DR: The cloning of cDNAs encoding glutamate receptor subunits, which occurred mainly between 1989 and 1992, stimulated the development of ionotropic glutamate receptors in the brain.
Abstract: The ionotropic glutamate receptors are ligand-gated ion channels that mediate the vast majority of excitatory neurotransmission in the brain. The cloning of cDNAs encoding glutamate receptor subunits, which occurred mainly between 1989 and 1992 ([Hollmann and Heinemann, 1994][1]), stimulated this
4,112 citations
TL;DR: This article showed that chronic intraventricular infusion of D,L-AP5 causes a selective impairment of place learning, which is highly sensitive to hippocampal damage, without affecting visual discrimination learning.
Abstract: Recent work has shown that the hippocampus contains a class of receptors for the excitatory amino acid glutamate that are activated by N-methyl-D-aspartate (NMDA) and that exhibit a peculiar dependency on membrane voltage in becoming active only on depolarization. Blockade of these sites with the drug aminophosphonovaleric acid (AP5) does not detectably affect synaptic transmission in the hippocampus, but prevents the induction of hippocampal long-term potentiation (LTP) following brief high-frequency stimulation. We now report that chronic intraventricular infusion of D,L-AP5 causes a selective impairment of place learning, which is highly sensitive to hippocampal damage, without affecting visual discrimination learning, which is not. The L-isomer of AP5 did not produce behavioural effects. AP5 treatment also suppressed LTP in vivo. These results suggest that NMDA receptors are involved in spatial learning, and add support to the hypothesis that LTP is involved in some, but not all, forms of learning.
3,488 citations
TL;DR: Recombinant binary NR1-NR2 channels show comparable Ca2+ permeabilities, but marked differences in voltage-dependent Mg2+ block and in offset decay time constants, which provide a basis for NMDA channel heterogeneity in the brain.
3,419 citations
TL;DR: This review discusses International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.
Abstract: The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.
3,044 citations
Cites background from "Magnesium gates glutamate-activated..."
...showing both fast and slow components (Nowak et al., 1984; Vargas-Caballero and Robinson, 2003, 2004; Kampa et al., 2004; Clarke and Johnson, 2006) with rates depending on the GluN2 subunit (Clarke and Johnson, 2006)....
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TL;DR: G glycine may facilitate excitatory transmission in the brain through an allosteric activation of the NMDA receptor, and can be observed in outside-out patches as an increase in the frequency of opening of the channels activated by NMDA agonists.
Abstract: Transmitters mediating 'fast' synaptic processes in the vertebrate central nervous system are commonly placed in two separate categories that are believed to exhibit no interaction at the receptor level. The 'inhibitory transmitters' (such as glycine and GABA) are considered to act only on receptors mediating a chloride conductance increase, whereas 'excitatory transmitters' (such as L-glutamate) are considered to activate receptors mediating a cationic conductance increase. The best known excitatory receptor is that specifically activated by N-methyl-D-aspartate (NMDA) which has recently been characterized at the single channel level. The response activated by NMDA agonists is unique in that it exhibits a voltage-dependent Mg block. We report here that this response exhibits another remarkable property: it is dramatically potentiated by glycine. This potentiation is not mediated by the inhibitory strychnine-sensitive glycine receptor, and is detected at a glycine concentration as low as 10 nM. The potentiation can be observed in outside-out patches as an increase in the frequency of opening of the channels activated by NMDA agonists. Thus, in addition to its role as an inhibitory transmitter, glycine may facilitate excitatory transmission in the brain through an allosteric activation of the NMDA receptor.
3,018 citations
References
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TL;DR: The extracellular patch clamp method, which first allowed the detection of single channel currents in biological membranes, has been further refined to enable higher current resolution, direct membrane patch potential control, and physical isolation of membrane patches.
Abstract: 1. The extracellular patch clamp method, which first allowed the detection of single channel currents in biological membranes, has been further refined to enable higher current resolution, direct membrane patch potential control, and physical isolation of membrane patches. 2. A description of a convenient method for the fabrication of patch recording pipettes is given together with procedures followed to achieve giga-seals i.e. pipette-membrane seals with resistances of 10(9) - 10(11) omega. 3. The basic patch clamp recording circuit, and designs for improved frequency response are described along with the present limitations in recording the currents from single channels. 4. Procedures for preparation and recording from three representative cell types are given. Some properties of single acetylcholine-activated channels in muscle membrane are described to illustrate the improved current and time resolution achieved with giga-seals. 5. A description is given of the various ways that patches of membrane can be physically isolated from cells. This isolation enables the recording of single channel currents with well-defined solutions on both sides of the membrane. Two types of isolated cell-free patch configurations can be formed: an inside-out patch with its cytoplasmic membrane face exposed to the bath solution, and an outside-out patch with its extracellular membrane face exposed to the bath solution. 6. The application of the method for the recording of ionic currents and internal dialysis of small cells is considered. Single channel resolution can be achieved when recording from whole cells, if the cell diameter is small (less than 20 micrometer). 7. The wide range of cell types amenable to giga-seal formation is discussed.
17,136 citations
01 Jan 1995
TL;DR: A Practical Guide to Patch Clamping R.H. Penner, C.W. Heinemann, and P. Jonas.
Abstract: A Practical Guide to Patch Clamping R. Penner. Tightseal Wholecell Recording A. Marty, E. Neher. Guide to Data Acquisition and Analysis S.H. Heinemann. Electronic Design of the Patch Clamp F.J. Sigworth. Low Noise Recording K. Benndorf. Voltage Offsets in Patch Clamp Experiments E. Neher. Techniques for Membrane Capacitance Measurements K.D. Gillis. Patch Pipette Recordings from the Soma, Dendrites and Axon of Neurons in Brain Slices B. Sakmann, G. Stuart. Patchclamp and Calcium Imaging in Brain Slices J. Eilers, et al. Fast Application of Agonists to Isolated Membrane Patches P. Jonas. Electrochemical Detection of Secretion from Single Cells R.H. Chow, L. von Ruden. Technical Approaches to Studying Specific Properties of Ion Channels in Plants R. Hedrich. The Giant Membrane Patch D.W. Hilgemann. A Fast Pressureclamp Technique for Studying Mechanogated Channels D.W. McBride, O.P. Hamill. Electrophysiological Recordings from Xenopus oocytes W. Stuhmer, A.B. Parekh. PCR Analysis of Ion Channel Expression in Single Neurons of Brain Slices H. Monyer, P. Jonas. 3 additional articles. Index.
2,592 citations
2,465 citations
TL;DR: A number of compounds related to TEA+ (tetraethylammoniumion) were injected into squid axons and their effects on g K (the potassium conductance) were determined, suggesting that K+ ions traverse the membrane by way of pores, and they cannot be explained by the usual type of carrier model.
Abstract: A number of compounds related to TEA(+) (tetraethylammoniumion) were injected into squid axons and their effects on g(K) (the potassium conductance) were determined. In most of these ions a quaternary nitrogen is surrounded by three ethyl groups and a fourth group that is very hydrophobic. Several of the ions cause inactivation of g(K), a type of ionic gating that is not normally seen in squid axon; i.e., after depolarization g(K) increases and then spontaneously decreases to a small fraction of its peak value even though the depolarization is maintained. Observations on the mechanism of this gating show that (a) QA (quaternary ammonium) ions only enter K(+) channels that have open activation gates (the normal permeability gates). (b) The activation gates of QA-occluded channels do not close readily. (c) Hyperpolarization helps to clear QA ions from the channels. (d) Raising the external K(+) concentration also helps to clear QA ions from the channels. Observations (c) and (d) strongly suggest that K(+) ions traverse the membrane by way of pores, and they cannot be explained by the usual type of carrier model. The data suggest that a K(+) pore has two distinct parts: a wide inner mouth that can accept a hydrated K(+) ion or a TEA(+)-like ion, and a narrower portion that can accept a dehydrated or partially dehydrated K(+) ion, but not TEA(+).
897 citations
TL;DR: It is concluded that drug molecules reversibly block open end‐plate channels and that the flickering within a burst represents this fast, repeatedly occurring reaction.
Abstract: 1. Single channel currents through acetylcholine receptor channels (ACh channels) were recorded at chronically denervated frog muscle extrajunctional membranes in the absence and presence of the lidocaine derivatives QX-222 and QX-314. 2. The current wave forms due to the opening and closing of single ACh channels (activated by suberyldicholine) normally are square pulses. These single pulses appear to be chopped into bursts of much shorter pulses, when the drug QX-222 is present in addition to the agonist. 3. The mean duration of the bursts is comparable to or longer than the normal channel open time, and increases with increasing drug concentration. 4. The duration of the short pulses within a burst decreases with increasing drug concentration. 5. It is concluded that drug molecules reversibly block open end-plate channels and that the flickering within a burst represents this fast, repeatedly occurring reaction. 6. The voltage dependence of the reaction rates involved, suggested that the site of the blocking reaction is in the centre of the membrane, probably inside the ionic channel.
850 citations