Selective activation of phosphoinositide hydrolysis by a rigid analogue of glutamate

1. The metabotropic glutamate (mGlu) response was investigated in dissociated rat hippocampal CAI pyramidal neurones using conventional and nystatin-perforated whole-cell modes of the patch recording configuration. 2. In the perforated patch recording configuration, the application of glutamate (Glu), quisqualate (QA), aspartate (Asp) and N-methyl-D-aspartate (NMDA) induced a slow outward current superimposed on a fast ionotropic inward current, whereas a-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and kainate (KA) induced only an ionotropic inward current at a holding potential (VH) of -20 mV. A specific agonist of the mGlu receptor (mGluR), trans-1-aminocyclopentane-1,3-dicarboxylate (tACPD), induced an outward current in -80 % of the neurones tested. Asp-and NMDA-induced outward currents were antagonized by D-2-amino-5-phosphonopentanoate (D-AP5) whereas Glu-, QA-and tACPD-induced outward currents were not antagonized by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 6,7-dinitroquinoxaline-2,3-dione (DNQX) and D-AP5, indicating that the mGlu response is an outward current component. 3. L-2-Amino-3-phosphonopropionate (L-AP3) and DL-2-amino-4-phosphonobutyrate (AP4) did not block the mGlu response. 4. The relative potencies of mGlu agonists were QA > Glu > tACPD. The threshold and EC50 values of metabotropic outward currents were 10-100 times lower than those of the ionotropic inward current (iGlu response).5. The reversal potential of the mGlu response (Emaju) was close to EK (K+ equilibrium potential), and it shifted 59*5 mV for a tenfold change in extracellular K+ concentration.6. In Ca2"-free external solution, the mGlu response was elicited by an initial application of Glu, but subsequent applications failed to induce the response. There was also an increase in the intracellular free Ca21 concentration ([Ca2+]1) during the application of Glu and QA but not of AMPA, indicating Ca2" release from an intracellular Ca2+ store. 7. During the activation of a Ca2"-dependent K+ current (IK(ca)) by inositol trisphosphate (IP3) in the internal solution, the mGlu response was suppressed. Addition of GDP-,b-S, neomycin or heparin to the internal solution also suppressed the mGlu response, but staurosporine had no effect. The mGlu response was abolished by pretreatment with either caffeine or ryanodine, but treatment with pertussis toxin (IAP) for 6-8 h had no effect.

Section: Discussionmentioning

confidence: 94%

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confidence: 99%

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confidence: 99%

See 1 more Smart Citation

Metabotropic glutamate response in acutely dissociated hippocampal CA1 pyramidal neurones of the rat.

Shirasaki

Harata

Akaike

1994

“…The responses in the present study were well maintained throughout the recording period (up to 1 h). Furthermore, we have been unable, so far, to detect resolvable single-channel currents under the patch pipette in cell-attached patches (not exposed to agonist) when the rest of the cell is exposed to either glutamate, quisqualate or trans-ACPD (trans-D,L-1-amino-1,3-cyclopentane-dicarboxylic acid), a selective agonist for the quisqualate 'metabotropic' receptor (Desai & Conn, 1990).…”

Section: Discussionmentioning

confidence: 99%

Activation of glutamate receptors and glutamate uptake in identified macroglial cells in rat cerebellar cultures.

Wyllie

Mathie

Symonds

et al. 1991

143

SUMMARY1. Patch-clamp methods have been used to examine the action of excitatory amino acids on three types of glial cell in cultures of rat cerebellum, namely type-ilike astrocytes, type-2 astrocytes and oligodendrocytes. In addition we have examined glutamate sensitivity of the precursor cell (the O-2A progenitor) that gives rise to type-2 astrocytes and oligodendrocytes.2. Glutamate (30 ftM), quisqualate (3-100 ,tM), (S)-a-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA, 10-30 /SM) and kainate (10-500 ,uM) were applied to cerebellar type-2 astrocytes examined under whole-cell voltage clamp. Each of these agonists induced inward currents in cells held at negative membrane potentials. The currents reversed direction near 0 mV holding potential. N-Methyl-D-aspartate (NMDA, 30-100 /,M) or aspartate (30 ,tM) in the presence of glycine (1 /1M) did not evoke any whole-cell current changes in type-2 astrocytes.3. The distribution of glutamate receptors in type-2 astrocytes was mapped with single-or double-barrelled ionophoretic pipettes containing quisqualate or kainate. Application of these agonists (current pulses 100 ms, 50-100 nA) to cells held at -60 mV evoked inward currents of 20-120 pA in the cell soma and 10-80 pA in the processes. Responses could also be obtained at the extremities of processes (-% 60 ,um from the soma). D. J. A. WYLLIE AND OTHERS type-1-like astrocytes were inhibited when external Na+ was replaced by Li', although Li+ was found to pass through the glutamate channel in type-2 astrocytes.6. Oligodendrocytes in cerebellar cultures did not respond to glutamate, quisqualate or kainate indicating a lack both of a detectable electrogenic glutamate uptake mechanism and of glutamate receptor ion channels in these cells.7. We conclude that, of the various macroglial cells, only the type-2 astrocyte and its progenitor cell possess 'fast' glutamate receptor channels in short-term ( < 4 day) cultures. Detectable uptake currents were confined to type-i-like astrocytes. However, in older cultures (> 7 day) type-I-like astrocytes also developed glutamate receptor channels, in addition to their uptake currents. The possible involvement of glial glutamate receptors and glutamate uptake in neuronal-glial interaction is considered.

“…Studies on the role of metabotropic receptors have proliferated since the compound trans-1 -aminocyclopentane-1,3-dicarboxylic acid (tACPD) was shown to be a selective agonist (Palmer, Monaghan & Cotman, 1989;Manzoni et al 1990;Desai & Conn, 1990). Activation of mGluR by tACPD or by quisqualate reduces potassium currents of hippocampal neurones (Charpak, Gahwiler, Do & Knopfel, 1990;Baskys, Bernstein, Barolet & Carlen, 1990).…”

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confidence: 99%

Metabotropic glutamate receptors mediate a post‐tetanic excitation of guinea‐pig hippocampal inhibitory neurones.

Miles

Poncer

1993

104

SUMMARY1. Inhibitory cell activity and inhibitory postsynaptic potentials impinging spontaneously on pyramidal cells were recorded in the CA3 region of hippocampal slices from guinea-pig. We compared the effects on synaptic inhibition, of tetanic stimuli in the presence of antagonists of ionotropic excitatory amino acid receptors, and of application of agonists of metabotropic glutamate receptors.2. Tetanic stimulation of afferent fibres caused an increase, of duration 0 52-5 min, in the frequency of spontaneous Cl--mediated IPSPs. Inhibitory cell firing increased due to a depolarization and a reduction of after-hyperpolarizing potentials.3. Tetanic stimulation induced, in some experiments, rhythmic bursts of IPSPs and transformed the firing pattern of some inhibitory cells from a discharge of single action potentials to rhythmic bursts of three to five action potentials.4. Application of the metabotropic glutamate receptor agonist, trans-1-aminocyclopentane-1,3-dicarboxylic acid (tACPD), at concentrations from 3-10/,M increased the frequency of spontaneous IPSPs. In some slices tACPD caused IPSPs to occur rhythmically. IPSP