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R Turecek

Publications and source records attributed to R Turecek.

7 recordsLinked to original sources
PubMed2004

Intracellular spermine decreases open probability of N-methyl-D-aspartate receptor channels.

Spermine and related polyamines have been shown to be endogenous regulators of several ion channel types including ionotropic glutamate receptors. The effect of spermine on N-methyl-d-aspartate (NMDA) receptors in cultured rat hippocampal neurons was studied using single-channel and whole-cell patch clamp recordings. Intracellular spermine resulted in the dose-dependent inhibition of NMDA-induced responses. Spermine reversibly inhibited the single NMDA receptor channel activity in inside-out patches suggesting a membrane-delimited mechanism of action. Open probability of NMDA receptor channels was decreased in a dose-dependent manner. Mechanism of spermine-induced inhibition of NMDA receptor was different from that of intracellular Ca(2+)-induced NMDA receptor inactivation. Both pharmacological studies and single channel analysis indicate that in contrast to the effect of extracellular spermine the intracellular spermine effect is not dependent on the NMDA receptor subunit composition. We propose that intracellular spermine has a direct inhibitory effect on NMDA receptors that is different from calcium-induced NMDA receptor inactivation and spermine-induced voltage-dependent inhibition of AMPA/kainate receptors. Spermine-induced tonic change in the open probability of NMDA receptor channels may play a role in mechanisms underlying short-term changes in the synaptic efficacy.

Animals↗
PubMed2001

Presynaptic glycine receptors enhance transmitter release at a mammalian central synapse.

Glycine and GABAA (gamma-aminobutyric acid A) receptors are inhibitory neurotransmitter-gated Cl- channels localized in postsynaptic membranes. In some cases, GABAA receptors are also found presynaptically, but they retain their inhibitory effect as their activation reduces excitatory transmitter release. Here we report evidence for presynaptic ionotropic glycine receptors, using pre- and postsynaptic recordings of a calyceal synapse in the medial nucleus of the trapezoid body (MNTB). Unlike the classical action of glycine, presynaptic glycine receptors triggered a weakly depolarizing Cl- current in the nerve terminal. The depolarization enhanced transmitter release by activating Ca2+ channels and increasing resting intraterminal Ca2+ concentrations. Repetitive activation of glycinergic synapses on MNTB neurons also enhanced glutamatergic synaptic currents, indicating that presynaptic glycine receptors are activated by glycine spillover. These results reveal a novel site of action of the transmitter glycine, and indicate that under certain conditions presynaptic Cl- channels may increase transmitter release.

Animals↗
PubMed2000

Control of synaptic depression by glutamate transporters.

The role of glutamate transporters in the regulation of synaptic depression was examined in the avian nucleus magnocellularis. Repetitive stimulation of presynaptic auditory nerve fibers resulted in acute depression of EPSCs. Pharmacological blockade of glutamate transport in glial cells enhanced residual glutamate in the synaptic cleft and markedly increased the extent of depression at stimulus frequencies above 20 Hz via a postsynaptic mechanism. Glutamate pyruvate transaminase, a glutamate scavenger, accelerated the decay of the EPSC and reduced synaptic depression, indicating that transporters are not completely effective in rapid removal of glutamate. Regulation of residual transmitter by glia may thus serve to control synaptic strength in a frequency-dependent manner.

ATP-Binding Cassette Transporters↗
PubMed1997

Spontaneous openings of NMDA receptor channels in cultured rat hippocampal neurons.

Spontaneous and N-methyl-D-aspartate (NMDA)-evoked single-channel currents were studied in outside-out patches isolated from cultured rat hippocampal neurons. Both spontaneous and NMDA-evoked single-channel currents reversed at potentials close to 0 mV and exhibited multiple amplitude levels of similar amplitude. Both spontaneous and NMDA-evoked single-channel currents were inhibited by Mg2+ in a voltage-dependent manner and by 7-chlorokynurenic acid. The activity of spontaneous single-channel currents was reduced by the competitive NMDA receptor antagonists, but by one to three orders of magnitude less than expected assuming that the spontaneous activity is due to an ambient NMDA receptor agonist present in the extracellular solution. Our results suggest that, similar to other ligand-gated ion channels, NMDA receptor channels have a dual mode of activation--spontaneous and agonist induced.

Animals↗
PubMed1997

[An NMDA glutamate receptor subtype].

Glutamate is the main excitatory synaptic transmitter between neurones in the central nervous system. The excitatory effect of glutamate is due to activation of two distinct types of receptor ion channels-AMPA/kainate and NMDA type. This article reviews recent discoveries concerning molecular structure of NMDA receptor channels, its pharmacology and biophysics including excitatory postsynaptic currents mediated by activation of this subtype of glutamate receptor.

Animals↗
PubMed1995

G-protein modulation of glycine-resistant NMDA receptor desensitization in rat cultured hippocampal neurons.

Activation of N-methyl-D-aspartate (NMDA) subtype glutamate receptors increases the excitability of most neurons within the CNS. A common feature of ionotropic glutamate receptors is their ability to undergo desensitization. In the present experiments we have examined the role of guanine nucleotide-binding proteins (G-proteins) in the regulation of NMDA receptor desensitization. Repeated NMDA receptor activation with 2 mM extracellular Ca2+ increased the degree of glycine-resistant NMDA receptor desensitization of subsequent responses to NMDA recorded in the presence of 0.2 mM Ca2+. The recovery of glycine-resistant NMDA receptor desensitization after repeated NMDA receptor activation in the presence of 2 mM Ca2+ was significantly reduced in neurons intracellularly dialysed with guanosine-5'-O-(3-thiotriphosphate), guanosine-5'-triphosphate or AlCl3 and CsF, compounds known to activate G-proteins. Intracellular dialysis with guanosine-5'-O-(2-thiodiphosphate), adenosine triphosphate, adenosine triphosphate, or adenosine-5'-O-(3-thiotriphosphate) was ineffective. The calcium permeability of NMDA receptor-channels was not altered by intracellular dialysis with GTP gamma S. This suggests that modulation of NMDA receptor desensitization by G-proteins represents a novel mechanism for regulation of glutamate-gated ion channel activity.

Animals↗