Synaptic NMDA receptor channels have a low open probability

C. Rosenmund, A. Feltz, Gary Westbrook

Research output: Contribution to journalArticle

129 Citations (Scopus)

Abstract

Realistic estimates of channel-gating parameters of synaptic receptors are essential to an understanding of synaptic transmission and modulation. However, the gating of N-methyl-D-aspartate (NMDA) channels appears to differ, depending on recording conditions; thus, it remains unclear what measurements are most relevant to synaptic receptors. To further explore this discrepancy, we examined the open probability (P(o)) of NMDA channels in whole-cell and outside-out patch recording from cultured hippocampal neurons. Currents were evoked by rapid application of saturating concentrations of NMDA in the presence or absence of the 'irreversible' open channel blocker, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine). The reduction of the peak amplitude and the acceleration of the decay of the current in MK-801 were used to derive P(o) by fitting the current traces to a multistate kinetic model. The P(o) in whole cell was low (0.04), similar to that previously measured for synaptically activated NMDA channels. In contrast, ensemble average currents from outside-out patches were much more rapidly blocked in the presence of MK-801, indicative of a significantly higher P(o). The P(o) also gradually increased with the duration of recording in both whole-cell and outside-out configurations, suggesting that channel gating is sensitive to mechanical alterations of the patch or that washout of cytoplasmic factors leads to an increase in channel open probability. To test whether the disparity in P(o) could be attributed to different gating of synaptic and extrasynaptic channels, the P(o) of whole-cell currents was measured before and after all synaptic NMDA channels (> 90%) were blocked by evoking EPSCs in the presence of MK-801. In microisland cultures containing a single excitatory neuron, 81 ± 4% of NMDA channels were synaptic. However, the P(o) of synaptic and extrasynaptic channels was equivalent, suggesting that P(o) recorded in the whole-cell configuration is the same as at the synapse. The low open probability for synaptic channels implies that with each presynaptic stimulus only 50% of channels that bind glutamate actually open; thus, the NMDA receptor-mediated EPSC has a significant functional 'reserve.'

Original languageEnglish (US)
Pages (from-to)2788-2795
Number of pages8
JournalJournal of Neuroscience
Volume15
Issue number4
StatePublished - 1995

Fingerprint

N-Methyl-D-Aspartate Receptors
N-Methylaspartate
Dizocilpine Maleate
Neurotransmitter Receptor
Neurons
Imines
Synaptic Transmission
Synapses
Glutamic Acid

Keywords

  • glutamate receptors
  • hippocampus
  • MK- 801
  • NMDA receptors
  • patch clamp
  • synaptic transmission

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Synaptic NMDA receptor channels have a low open probability. / Rosenmund, C.; Feltz, A.; Westbrook, Gary.

In: Journal of Neuroscience, Vol. 15, No. 4, 1995, p. 2788-2795.

Research output: Contribution to journalArticle

Rosenmund, C, Feltz, A & Westbrook, G 1995, 'Synaptic NMDA receptor channels have a low open probability', Journal of Neuroscience, vol. 15, no. 4, pp. 2788-2795.
Rosenmund, C. ; Feltz, A. ; Westbrook, Gary. / Synaptic NMDA receptor channels have a low open probability. In: Journal of Neuroscience. 1995 ; Vol. 15, No. 4. pp. 2788-2795.
@article{e372630aa0e74306998985397aee6d32,
title = "Synaptic NMDA receptor channels have a low open probability",
abstract = "Realistic estimates of channel-gating parameters of synaptic receptors are essential to an understanding of synaptic transmission and modulation. However, the gating of N-methyl-D-aspartate (NMDA) channels appears to differ, depending on recording conditions; thus, it remains unclear what measurements are most relevant to synaptic receptors. To further explore this discrepancy, we examined the open probability (P(o)) of NMDA channels in whole-cell and outside-out patch recording from cultured hippocampal neurons. Currents were evoked by rapid application of saturating concentrations of NMDA in the presence or absence of the 'irreversible' open channel blocker, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine). The reduction of the peak amplitude and the acceleration of the decay of the current in MK-801 were used to derive P(o) by fitting the current traces to a multistate kinetic model. The P(o) in whole cell was low (0.04), similar to that previously measured for synaptically activated NMDA channels. In contrast, ensemble average currents from outside-out patches were much more rapidly blocked in the presence of MK-801, indicative of a significantly higher P(o). The P(o) also gradually increased with the duration of recording in both whole-cell and outside-out configurations, suggesting that channel gating is sensitive to mechanical alterations of the patch or that washout of cytoplasmic factors leads to an increase in channel open probability. To test whether the disparity in P(o) could be attributed to different gating of synaptic and extrasynaptic channels, the P(o) of whole-cell currents was measured before and after all synaptic NMDA channels (> 90{\%}) were blocked by evoking EPSCs in the presence of MK-801. In microisland cultures containing a single excitatory neuron, 81 ± 4{\%} of NMDA channels were synaptic. However, the P(o) of synaptic and extrasynaptic channels was equivalent, suggesting that P(o) recorded in the whole-cell configuration is the same as at the synapse. The low open probability for synaptic channels implies that with each presynaptic stimulus only 50{\%} of channels that bind glutamate actually open; thus, the NMDA receptor-mediated EPSC has a significant functional 'reserve.'",
keywords = "glutamate receptors, hippocampus, MK- 801, NMDA receptors, patch clamp, synaptic transmission",
author = "C. Rosenmund and A. Feltz and Gary Westbrook",
year = "1995",
language = "English (US)",
volume = "15",
pages = "2788--2795",
journal = "Journal of Neuroscience",
issn = "0270-6474",
publisher = "Society for Neuroscience",
number = "4",

}

TY - JOUR

T1 - Synaptic NMDA receptor channels have a low open probability

AU - Rosenmund, C.

AU - Feltz, A.

AU - Westbrook, Gary

PY - 1995

Y1 - 1995

N2 - Realistic estimates of channel-gating parameters of synaptic receptors are essential to an understanding of synaptic transmission and modulation. However, the gating of N-methyl-D-aspartate (NMDA) channels appears to differ, depending on recording conditions; thus, it remains unclear what measurements are most relevant to synaptic receptors. To further explore this discrepancy, we examined the open probability (P(o)) of NMDA channels in whole-cell and outside-out patch recording from cultured hippocampal neurons. Currents were evoked by rapid application of saturating concentrations of NMDA in the presence or absence of the 'irreversible' open channel blocker, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine). The reduction of the peak amplitude and the acceleration of the decay of the current in MK-801 were used to derive P(o) by fitting the current traces to a multistate kinetic model. The P(o) in whole cell was low (0.04), similar to that previously measured for synaptically activated NMDA channels. In contrast, ensemble average currents from outside-out patches were much more rapidly blocked in the presence of MK-801, indicative of a significantly higher P(o). The P(o) also gradually increased with the duration of recording in both whole-cell and outside-out configurations, suggesting that channel gating is sensitive to mechanical alterations of the patch or that washout of cytoplasmic factors leads to an increase in channel open probability. To test whether the disparity in P(o) could be attributed to different gating of synaptic and extrasynaptic channels, the P(o) of whole-cell currents was measured before and after all synaptic NMDA channels (> 90%) were blocked by evoking EPSCs in the presence of MK-801. In microisland cultures containing a single excitatory neuron, 81 ± 4% of NMDA channels were synaptic. However, the P(o) of synaptic and extrasynaptic channels was equivalent, suggesting that P(o) recorded in the whole-cell configuration is the same as at the synapse. The low open probability for synaptic channels implies that with each presynaptic stimulus only 50% of channels that bind glutamate actually open; thus, the NMDA receptor-mediated EPSC has a significant functional 'reserve.'

AB - Realistic estimates of channel-gating parameters of synaptic receptors are essential to an understanding of synaptic transmission and modulation. However, the gating of N-methyl-D-aspartate (NMDA) channels appears to differ, depending on recording conditions; thus, it remains unclear what measurements are most relevant to synaptic receptors. To further explore this discrepancy, we examined the open probability (P(o)) of NMDA channels in whole-cell and outside-out patch recording from cultured hippocampal neurons. Currents were evoked by rapid application of saturating concentrations of NMDA in the presence or absence of the 'irreversible' open channel blocker, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine). The reduction of the peak amplitude and the acceleration of the decay of the current in MK-801 were used to derive P(o) by fitting the current traces to a multistate kinetic model. The P(o) in whole cell was low (0.04), similar to that previously measured for synaptically activated NMDA channels. In contrast, ensemble average currents from outside-out patches were much more rapidly blocked in the presence of MK-801, indicative of a significantly higher P(o). The P(o) also gradually increased with the duration of recording in both whole-cell and outside-out configurations, suggesting that channel gating is sensitive to mechanical alterations of the patch or that washout of cytoplasmic factors leads to an increase in channel open probability. To test whether the disparity in P(o) could be attributed to different gating of synaptic and extrasynaptic channels, the P(o) of whole-cell currents was measured before and after all synaptic NMDA channels (> 90%) were blocked by evoking EPSCs in the presence of MK-801. In microisland cultures containing a single excitatory neuron, 81 ± 4% of NMDA channels were synaptic. However, the P(o) of synaptic and extrasynaptic channels was equivalent, suggesting that P(o) recorded in the whole-cell configuration is the same as at the synapse. The low open probability for synaptic channels implies that with each presynaptic stimulus only 50% of channels that bind glutamate actually open; thus, the NMDA receptor-mediated EPSC has a significant functional 'reserve.'

KW - glutamate receptors

KW - hippocampus

KW - MK- 801

KW - NMDA receptors

KW - patch clamp

KW - synaptic transmission

UR - http://www.scopus.com/inward/record.url?scp=0028965220&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0028965220&partnerID=8YFLogxK

M3 - Article

VL - 15

SP - 2788

EP - 2795

JO - Journal of Neuroscience

JF - Journal of Neuroscience

SN - 0270-6474

IS - 4

ER -