Biomedical subjects

U Gerber

Publications and source records attributed to U Gerber.

At least 19 recordsLinked to original sources

PubMed2001

Fast synaptic transmission mediated by P2X receptors in CA3 pyramidal cells of rat hippocampal slice cultures.

1. A fast ATP-mediated synaptic current was identified in CA3 pyramidal cells in organotypic hippocampal slice cultures. In the presence of inhibitors for ionotropic glutamate and GABA receptors, extracellular stimulation in the pyramidal cell layer evoked fast synaptic currents that reversed near 0 mV, reflecting an increase in a non-selective cationic conductance. This response was mimicked by focal application of ATP. Antagonists of ionotropic P2X receptors reduced both synaptic and ATP-induced currents. 2. Using a pharmacological approach, the source of synaptically released ATP was determined. Synaptic ATP responses were insensitive to presynaptic blockade of GABAergic transmission between interneurons and CA3 pyramidal cells with the mu-opioid receptor agonist D-Ala(2),MePhe(4),Met(O)(5)-ol-enkephalin (FK33-824), but were blocked by adenosine, which inhibits glutamate release from synaptic terminals in the hippocampus. However, selective inhibition of mossy fibre glutamatergic transmission with the metabotropic glutamate receptor group II agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG IV) did not affect the response. This result points to the associational fibres as the source of the ATP-mediated synaptic response. 3. These results suggest that ATP, coreleased with glutamate, induces a synaptic response in CA3 pyramidal cells that is observed mainly under conditions of synchronous discharge from multiple presynaptic inputs.

Adenosine Triphosphate↗

PubMed2000

Acute decrease in net glutamate uptake during energy deprivation.

The extracellular glutamate concentration ([glu](o)) rises during cerebral ischemia, reaching levels capable of inducing delayed neuronal death. The mechanisms underlying this glutamate accumulation remain controversial. We used N-methyl-D-aspartate receptors on CA3 pyramidal neurons as a real-time, on-site, glutamate sensor to identify the source of glutamate release in an in vitro model of ischemia. Using glutamate and L-trans-pyrrolidine-2,4-dicarboxylic acid (tPDC) as substrates and DL-threo-beta-benzyloxyaspartate (TBOA) as an inhibitor of glutamate transporters, we demonstrate that energy deprivation decreases net glutamate uptake within 2-3 min and later promotes reverse glutamate transport. This process accounts for up to 50% of the glutamate accumulation during energy deprivation. Enhanced action potential-independent vesicular release also contributes to the increase in [glu](o), by approximately 50%, but only once glutamate uptake is inhibited. These results indicate that a significant rise in [glu](o) already occurs during the first minutes of energy deprivation and is the consequence of reduced uptake and increased vesicular and nonvesicular release of glutamate.

2-Amino-5-phosphonovalerate↗

PubMed2000

G-protein-independent signaling by G-protein-coupled receptors.

Two classes of receptors transduce neurotransmitter signals: ionotropic receptors and heptahelical metabotropic receptors. Whereas the ionotropic receptors are structurally associated with a membrane channel, a mediating mechanism is necessary to functionally link metabotropic receptors with their respective effectors. According to the accepted paradigm, the first step in the metabotropic transduction process requires the activation of heterotrimeric G-proteins. An increasing number of observations, however, point to a novel mechanism through which neurotransmitters can initiate biochemical signals and modulate neuronal excitability. According to this mechanism metabotropic receptors induce responses by activating transduction systems that do not involve G-proteins.

Animals↗

PubMed1999

Inhibition of uptake unmasks rapid extracellular turnover of glutamate of nonvesicular origin.

Maintaining glutamate at low extracellular concentrations in the central nervous system is necessary to protect neurons from excitotoxic injury and to ensure a high signal-to-noise ratio for glutamatergic synaptic transmission. We have used DL-threo-beta-benzyloxyaspartate (TBOA), an inhibitor of glutamate uptake, to determine the role of glutamate transporters in the regulation of extracellular glutamate concentration. By using the N-methyl-D-aspartate receptors of patched CA3 hippocampal neurons as "glutamate sensors," we observed that application of TBOA onto organotypic hippocampal slices led to a rapid increase in extracellular glutamate concentration. This increase was Ca(2+)-independent and was observed in the presence of tetrodotoxin. Moreover, prevention of vesicular glutamate release with clostridial toxins did not affect the accumulation of glutamate when uptake was inhibited. Inhibition of glutamine synthase, however, increased the rate of accumulation of extracellular glutamate, indicating that glial glutamate stores can serve as a source in this process. TBOA blocked synaptically evoked transporter currents in astrocytes without inducing a current mediated by the glutamate transporter. This indicates that this inhibitor is not transportable and does not release glutamate by heteroexchange. These results show that under basal conditions, the activity of glutamate transporters compensates for the continuous, nonvesicular release of glutamate from the intracellular compartment. As a consequence, acute disruption of transporter activity immediately results in significant accumulation of extracellular glutamate.

ATP-Binding Cassette Transporters↗

PubMed1999

Involvement of the N-methyl-D-aspartate receptor in neuronal cell death induced by cytotoxic T cell-derived secretory granules.

The mechanisms underlying neurotoxicity mediated by cytotoxic T lymphocytes (CTL) and their secretory granule proteins perforin and granzymes remain unclear. We evaluated the possible role of the neurotransmitter glutamate in cell death observed in differentiated neurons exposed to CTL-derived granules. Excitotoxicity induced by excessive concentrations of extracellular glutamate is associated with a rise in intracellular calcium and can lead to generation of NO through the activation of glutamatergic N-methyl-D-aspartate (NMDA) receptors. Consistent with an involvement of glutamate, we found that cell death in mature cerebral granule cells was inhibited by 65-80% by two NMDA receptor blockers (MK-801 and D-2-amino-5-phosphonovaleric acid) or a NO synthase blocker (N(G)-nitro-L-arginine methylester). Furthermore, neurons treated with secretory granules responded with a biphasic rise in the intracellular calcium concentration ([Ca2+]i). Whereas MK-801 did not interfere with the immediate rise of [Ca2+]i, the second wave of calcium accumulation starting at 40 min was delayed by 20 min and reduced in amplitude in the presence of MK-801. In immature, NMDA receptor-negative neurons, MK-801 prevented neither the cytotoxicity nor the calcium influx observed 5 min after addition of cytotoxic granules. The demonstration that NMDA receptors and NO are involved in granule-mediated killing of mature neurons opens new avenues in the treatment of neuronal cell death in CTL-mediated diseases such as viral encephalitis.

2-Amino-5-phosphonovalerate↗

PubMed1999

G-protein-independent signaling mediated by metabotropic glutamate receptors.

Synaptically released glutamate activates ionotropic and metabotropic receptors at central synapses. Metabotropic glutamate receptors (mGluRs) are thought to modulate membrane conductances through transduction cascades involving G proteins. Here we show, in CA3 pyramidal cells from rat hippocampus, that synaptic activation of type 1 mGluRs by mossy fiber stimulation evokes an excitatory postsynaptic response independent of G-protein function, while inhibiting an afterhyperpolarization current through a G-protein-coupled mechanism. Experiments using peptide activators and specific inhibitors identified a Src-family protein tyrosine kinase as a component of the G-protein-independent transduction pathway. These results represent the first functional evidence for a dual signaling mechanism associated with a heptahelical receptor such as mGluR1, in which intracellular transduction involves activation of either G proteins or tyrosine kinases.

ATP-Binding Cassette Transporters↗

PubMed1999

Apamin-sensitive conductance mediates the K(+) current response during chemical ischemia in CA3 pyramidal cells.

Pyramidal cells typically respond to ischemia with initial transient hyperpolarization, which may represent a neuroprotective response. To identify the conductance underlying this hyperpolarization in CA3 pyramidal neurons of rat hippocampal organotypic slice cultures, recordings were obtained using the single-electrode voltage-clamp technique. Brief chemical ischemia (2 mM 2-deoxyglucose and 3 mM NaN(3), for 4 min) induced a response mediated by an increase in K(+) conductance. This current was blocked by intracellular application of the Ca(2+) chelator, bis-(o-aminophenoxy)-N,N,N', N'-tetraacetic acid (BAPTA), reduced with low external [Ca(2+)], and inhibited by a selective L-type Ca(2+) channel inhibitor, isradipine, consistent with the activation of a Ca(2+)-dependent K(+) conductance. Experiments with charybdotoxin (10 nM) and tetraethylammonium (TEA; 1 mM), or with the protein kinase C activator, phorbol 12,13-diacetate (PDAc; 3 microM), ruled out an involvement of a large conductance-type or an apamin-insensitive small conductance, respectively. In the presence of apamin (1 microM), however, the outward current was significantly reduced. These results demonstrate that in rat hippocampal CA3 pyramidal neurons an apamin-sensitive Ca(2+)-dependent K(+) conductance is activated in response to brief ischemia generating a pronounced outward current.

ATP-Binding Cassette Transporters↗

PubMed1998

Effects of transient oxygen-glucose deprivation on G-proteins and G-protein-coupled receptors in rat CA3 pyramidal cells in vitro.

The role of guanosine triphosphate-binding proteins (G-proteins) in the generation of the outward current during transient oxygen-glucose deprivation (OGD) was investigated in CA3 pyramidal cells in rat hippocampal organotypic slice cultures using the single-electrode voltage-clamp technique with KMeSO4-filled microelectrodes. To simulate ischaemia, brief chemical OGD (2 mM 2-deoxyglucose and 3 mM NaN3 for 4-9 min) was used, which induced an outward K+ current associated with an increase in input conductance. OGD failed to induce the outward current under conditions where G-protein function was disrupted by loading cells with guanosine 5'-O-(2-thiodiphosphate) [GDPbetaS] or after prolonged injection of guanosine 5'-O(3-thiotdphosphate) [GTPgammaS]. However, in slices treated with pertussis toxin (PTX), OGD still elicited the outward current, indicating that PTX-insensitive G-proteins are involved. Consistent with this insensitivity to PTX, neither adenosine receptors nor GABA(B) (gamma-aminobutyric acid) receptors, which operate via PTX-sensitive G-proteins, mediate the OGD-induced outward current. When adenosine receptors or GABA(B) receptors were blocked with 1,3-dipropyl-8-psulphophenylxanthine (DPSPX, 5 microM) or CGP 52 432 (10 microM), respectively, the OGD-induced response was not modified. The response also persisted following pretreatment of slice cultures with tetanus toxin to prevent vesicular release of neurotransmitters and neuromodulators from presynaptic terminals. Both PTX-sensitive and PTX-insensitive G-protein-mediated responses were suppressed during OGD. The inward current induced by the metabotropic glutamate receptor agonist 1 S, 3R-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD) and the outward current elicited by adenosine or baclofen were strongly or completely attenuated. In contrast, the ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) response was not affected. These findings suggest that during OGD there is a functional uncoupling of receptors from G-proteins, and a direct receptor-independent activation of PTX-insensitive G-proteins leading to an increase in membrane K+ conductance.

Adenosine↗

PubMed1998

L-Type Ca2+ channels mediate the slow Ca2+-dependent afterhyperpolarization current in rat CA3 pyramidal cells in vitro.

Single-electrode voltage-clamp recordings were obtained from CA3 pyramidal cells in rat hippocampal organotypic slice cultures, and the slow Ca2+-dependent K+ current or afterhyperpolarization current (IAHP) was elicited with brief depolarizing voltage jumps. The slow IAHP was suppressed by the selective L-type Ca2+ channel antagonists isradipine (2 microM) or nifedipine (10 microM). In contrast, neither omega-conotoxin MVIIA (1 microM) nor omega-agatoxin IVA (200 nM), N-type and P/Q-type Ca2+ channel antagonists, respectively, attenuated this slow outward current. The slow IAHP was significantly reduced by thapsigargin (10 microM), a Ca2+ ATPase inhibitor that depletes intracellular Ca2+ stores, and by ryanodine (10-100 microM), which blocks Ca2+-induced Ca2+ release from intracellular compartments. At this concentration thapsigargin did not modify high-threshold Ca2+ current, which was, however, blocked by isradipine. Thus, in hippocampal CA3 pyramidal cells, Ca2+ influx through L-type Ca2+ channels is necessary to trigger the slow IAHP. Furthermore, intracellular Ca2+-activated Ca2+ stores represent a critical component in the transduction pathway leading to the generation of the slow IAHP.

Animals↗

PubMed1997

G-protein-mediated desensitization of metabotropic glutamatergic and muscarinic responses in CA3 cells in rat hippocampus.

1. Desensitization of a metabotropic response was investigated in CA3 pyramidal neurons in hippocampal slice cultures using the patch-clamp technique. 2. 1S,3R-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD), an agonist at metabotropic glutamate receptors (mGluRs), and metacholine (MCh), an agonist at muscarinic receptors, induced a cationic current that appears to be activated through a G-protein-independent transduction process, as previously shown. Prolonged or repetitive bath application of agonists led to rapid desensitization of the cationic current with a time constant of approximately 20 s. 3. Complete recovery from desensitization was observed within 6 min. 4. These responses mediated by mGluRs and muscarinic receptors cross-desensitized. 5. Preventing the activation of G-proteins by loading cells with GDP beta S strongly reduced or suppressed desensitization, and resulted in a sustained inward cationic current. When cells were filled with GTP gamma S to irreversibly activate G-proteins, the desensitization process was enhanced such that a first application of agonist caused a markedly reduced response. 6. These results show that a cationic current induced by metabotropic agonists in hippocampal pyramidal cells undergoes apparent desensitization and suggests that this process occurs through a G-protein-mediated inhibition of the underlying membrane conductance.

Animals↗

PubMed1997

1S, 3R-ACPD induces a region of negative slope conductance in the steady-state current-voltage relationship of hippocampal pyramidal cells.

Synaptic responses mediated by metabotropic glutamate receptors (mGluRs) display a marked voltage-dependent increase in amplitude when neurons are moderately depolarized beyond membrane potential. We have investigated the basis for this apparent nonlinear behavior by activating mGluRs with 1S, 3R-1-aminocyclopentane-1, 3-dicarboxylate (1S, 3R-ACPD; 10 microM) in CA3 pyramidal cells from rat hippocampal slice cultures with the use of the single-electrode voltage-clamp technique. Under control conditions, cells depolarized from resting potential by 10-20 mV responded with delayed outwardly rectifying currents due to activation of voltage- and Ca(2+)-dependent K+ conductances. In contrast, in the continuous presence of 1S, 3R-ACPD, small depolarizations (10-20 mV) induced a delayed inward current. The steady-state current-voltage relationship for this response displayed a region of negative slope conductance at potentials between -55 and -40 mV. The reversal potential of the corresponding 1S,3R-ACPD-sensitive tail currents (-93.0 +/- 2.2 mV, mean +/- SE) was close to the potassium reversal potential, consistent with an mGluR-mediated suppression of K+ current. When external K+ concentration was increased to 8 mM, there was a positive shift in reversal potential to -76.9 +/- 5.1 mV. The depolarization-induced inward current in the presence of 1S,3R-ACPD was blocked by Ba2+ (1 mM). The response was not dependent on changes in intracellular Ca2+ concentration and was insensitive to bath-applied Cs+ (1 mM), ruling out a contribution of Ca(2+)-dependent currents or the inward rectifier lQ. Furthermore, the effect of 1S,3R-ACPD was not mimicked by inhibiting afterhyperpolarizing current and M current with low-Ca2+ saline (0.5 mM Ca2+, 10 mM Mg2+) containing 10 mM tetraethylammonium chloride. A comparison of the responses induced by 1S,3R-ACPD and N-methyl-D-aspartate showed that both induce an inward current with small depolarizations from resting potential but with different kinetics and Mg2+ sensitivity. These results indicate that the suppression of K+ currents in response to activation of mGluRs is markedly voltage dependent, increasing at depolarized potentials and decreasing at hyperpolarized potentials. The negative slope conductance at membrane voltages positive to resting potential may underlie the amplification of mGluR-mediated responses when the membrane potential approaches action potential threshold.

Animals↗

PubMed1996

A slowly inactivating potassium current in CA3 pyramidal cells of rat hippocampus in vitro.

The time- and voltage-dependent properties of a slowly inactivating K+ current were investigated by using the single-electrode current- and voltage-clamp recording technique in CA3 hippocampal cells of organotypic slice cultures. After a period of prolonged hyperpolarization, the onset of action-potential discharge in response to depolarizing current injection was delayed by several seconds. The conductances underlying this delay were identified in voltage-clamp recordings. A biphasically decaying outward current was evoked when the membrane potential was stepped back to -60 mV after a 30 sec period of hyperpolarization. The fast component was identified as the previously described D-current and was blocked by 100 microM 4-aminopyridine (4-AP). The slow component, which we refer to as IK(slow), appeared to be mediated by K+ ions, because its reversal potential shifted in a Nernstian manner with changes in extracellular K+ concentration. It decayed with a time constant of 7.5 sec and required a hyperpolarizing prepulse below -95 mV for 5.5 sec for 50% recovery from inactivation. IK(slow) was found to be voltage-dependent, with 50% activation occurring at -65 mV and 50% steady-state inactivation occurring at -84 mV. It displayed minimal or no sensitivity to the K(+)-channel blockers 4-AP (0.1-5 mM), Cs+ (1 mM), tetraethylammonium (10-50 mM), Ba2+ (1 mM), dendrotoxin-alpha (5-10 microM), charybdotoxin (0.5-2.5 microM), or glibenclamide (5-10 microM) and was not affected by preventing increases in intracellular Ca2+ concentration with Ca2+ chelators. IK(slow) was reduced by activation of metabotropic glutamatergic and cholinergic receptors. In summary, the biophysical characteristics of IK(slow) suggest a role in determining discharge onset after a period of membrane hyperpolarization, and its modulation by G-protein-coupled receptors reveals an additional function for these receptors in the control of cellular excitability.

4-Aminopyridine↗

PubMed1996

Influence of gelatin matrices cross-linked with transglutaminase on the properties of an enclosed bioactive material using beta-galactosidase as model system.

Transglutaminase (protein-glutamine: amine gamma-glutamyltransferase, EC 2.3.2.13) from Streptoverticillium mobaraense has been used to stabilize immobilisates produced with beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) from Aspergillus oryzae and acid-processed gelatins of different qualities as support. The isopeptide level of N epsilon-(gamma-L-glutamyl)-L-lysine bonds formed by transglutaminase was determined to estimate their influence on the kinetic properties of the enclosed beta-galactosidase. An HPLC procedure using precolumn derivatization of the gelatin hydrolysates with FMOC-chloride was chosen which permits the analysis of cross-linked lysine with satisfactory precision. Depending on the gelatin quality, the degree of cross-links necessary for the transformation of gelatin into an insoluble protein was in the range 0.3-32.3% of the available lysine residues. beta-Galactosidase was entrapped in the gelatin matrices with a yield of 8-46% of the initial activity. Long reaction times for cross-linking were due to low yields rather than to the number of isopeptide bonds. Repeated use of the immobilisates did not lead to an appreciable loss of activity. The Vmax of beta-galactosidase were diminished by immobilization caused by a tighter package of the protein chains rather than by the extent of cross-links, while the obtained Km values of the free enzyme and the immobilisates were quite similar. Also, the pH and temperature of optima of the free enzyme and the gelatin immobilisates differ only slightly. The data suggest that the immobilization procedure only moderately affects the activity of enzymes catalysing the reaction of a small compound if gelatin with high jelly strength is cross-linked in a 10% solution with transglutaminase.

Aspergillus oryzae↗

PubMed1996

Glycine-mediated inhibitory postsynaptic potentials in the medial pontine reticular formation of the rat in vitro.

Glycinergic neurotransmission was examined in rat medial pontine reticular formation neurons in vitro. Intracellular recordings using glass microelectrodes were made in acutely prepared brainstem slices 400 microns thick. Spontaneous and electrically evoked synaptic activity was blocked by the glycine antagonist strychnine (1-5 microM) but not by the GABA antagonists bicuculline methiodide (40 microM) or picrotoxin (40 microM). Strychnine-sensitive spontaneous and evoked postsynaptic potentials persisted in the presence of the glutamate antagonist (kynurenate, 1 mM). Whole-cell voltage-clamp recordings were carried out in organotypic cultures of rat brainstem. The reversal potential of synaptic currents and responses to exogenously applied glycine were similar and were sensitive to manipulations of the chloride equilibrium potential. Synaptic activity but not responses to exogenous glycine were blocked by tetrodotoxin (0.3 microM). These results indicate the presence of robust, chloride ion-mediated glycinergic inhibition of medial pontine reticular formation neurons, and suggest that glycinergic neurons play an important role in controlling pontine premotor circuitry.

Animals↗

PubMed1995

Activation of a nonselective cationic conductance by metabotropic glutamatergic and muscarinic agonists in CA3 pyramidal neurons of the rat hippocampus.

We have characterized a cationic membrane conductance activated by metabotropic glutamatergic and muscarinic cholinergic agonists in CA3 neurons in hippocampal slice cultures using the patch-clamp technique. When the potassium concentration in the superfusing fluid was raised above 5 mM, a biphasic current was observed in cells held at -60 mV in response to stimulation of postsynaptic metabotropic glutamate receptors (mGluRs) with 1S,3R-ACPD (50 microM) or muscarinic receptors with methacholine (MCh, 5 microM). The initial inward component was due to an increase in a cationic membrane conductance as determined by its reversal potential and its sensitivity to changes in extracellular K+ or Na+. The conductance underlying this current displayed no apparent voltage sensitivity over the range -120 to -50 mV. The response was reduced by extracellular application of Ba2+, Cd2+, Mg2+, or TEA, whereas extracellular Cs+ or loading cells with BAPTA or Cs+ did not affect the current. The effects of 1S,3R-ACPD were reversibly inhibited by bath-applied MCPG, an antagonist at mGluRs. Experiments with atropine and pirenzepine indicated that non-M1 muscarinic receptors mediated the MCh-induced current. A decrease in a resting leak potassium conductance (IK,leak) was responsible for the late component of the 1S,3R-ACPD- and MCh-induced response, seen as an outward current in the bathing solution with high K+ concentration. Loading cells with GDP beta S, GTP gamma S, or GTP did not alter the cationic current, while, in the same cells, the reduction in IKleak was abolished or irreversibly activated. Single-channel recordings of cationic channel activity in the cell-attached configuration provided evidence for the requirement of second messengers in coupling these receptors to the cationic channels. The data indicate that in addition to the previously described reduction of IK,leak, IM, and IAHP, both 1S,3R-ACPD and MCh activate a nonselective cationic conductance that is clearly revealed upon elevating external K+ concentration. This current is mediated by activation of metabotropic receptors, although no evidence could be obtained to show an involvement of G-proteins.

Animals↗

PubMed1994

A rapid and simple method for the purification of transglutaminase from Streptoverticillium mobaraense.

Transglutaminase from Streptoverticillium mobaraense was partially purified by ion-exchange chromatography on a weak acid material and hydrophobic chromatography. The separation with a strong acid ion-exchanger produces homogeneous transglutaminase, in a single step and with high yields, directly from the centrifuged and filtered culture fluid of the micro-organism. The procedure reproduced several times could be also carried out on a larger scale with the optimized parameters of the laboratory isolations. The purified enzyme demonstrated good storage stability.

Chromatography, Ion Exchange↗

PubMed1994

Reduction of resting K+ current by metabotropic glutamate and muscarinic receptors in rat CA3 cells: mediation by G-proteins.

1. Effects of 1S,3R-1-aminocyclopentane-1,3-dicarboxylate (1S,3R-ACPD) acting at metabotropic glutamate receptors (mGluRs), and methacholine (MCh), acting at cholinergic muscarinic receptors, were investigated in CA3 neurones in hippocampal slice cultures using the patch-clamp technique. 2. Both 1S,3R-ACPD (10 microM) and MCh (0.5 microM) activated an inward current associated with a decrease in membrane conductance. The current was observed when the slow calcium-dependent after-hyperpolarizing current (IAHP) and the voltage-dependent current (IM) were not activated, reversed close to the reversal potential for K+ (EK) (Erev = -92.8 +/- 10.7 and -89.2 +/- 8.6 mV for 1S,3R-ACPD and MCh, respectively), varied linearly with membrane potential, and thus corresponds to a leak K+ current. 3. The decrease in K+ conductance elicited with 1S,3R-ACPD (50 microM) was substantially reduced (> 70%) with bath application of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG, 1 mM), a selective mGluR antagonist and was not mimicked by the enantiomer 1R,3S-ACPD (100 microM). 4. The effects of 1S,3R-ACPD and MCh were mediated by activation of G-proteins since no inward current could be elicited in GDP beta S-loaded cells (500 microM). When cells were dialysed with GTP (100 microM) or GTP gamma S (250 microM), however, the amplitude of the current was significantly enhanced. 5. These findings provide evidence that G-proteins couple the activation of mGluRs and muscarinic receptors to a decrease in leak K+ conductance.

Animals↗

PubMed1994

Potentiation of a metabotropic glutamatergic response following NMDA receptor activation in rat hippocampus.

Interactions between metabotropic glutamate and N-methyl-D-aspartate (NMDA) receptor-mediated responses were investigated in hippocampal CA3 cells using the single electrode voltage-clamp method. Bath application (2.5-10 microM, 30 s) or iontophoresis of 1-amino-cyclopentyl-trans-1S,3R-dicarboxylate (ACPD), a selective agonist for metabotropic glutamate receptors, resulted in an inward current associated with a decrease in membrane conductance. Following transient bath application of NMDA (5-10 microM, 30-60 s), the ACPD-induced inward current was potentiated for a period of up to 25 min (by 61 +/- 8% with bath application, by 32 +/- 15% with iontophoresis). Transient application of NMDA did not result in a potentiation of ionotropic RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or metabotropic muscarinic responses. ACPD responses were not potentiated following transient AMPA application. Intracellular buffering of calcium with tetrapotassium bis(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) prevented potentiation by NMDA in all cells. Bath application of arachidonic acid did not mimic the NMDA-induced potentiation. These results demonstrate that activation of NMDA receptors can specifically induce a long-lasting potentiation of a metabotropic glutamatergic response in hippocampal CA3 pyramidal cells. The characterization of this interaction may contribute to the elucidation of the physiological significance of metabotropic glutamate receptors.

Animals↗