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C W Christine

Publications and source records attributed to C W Christine.

10 recordsLinked to original sources
PubMed1998

Activity differentially regulates the surface expression of synaptic AMPA and NMDA glutamate receptors.

Distinct subtypes of glutamate receptors often are colocalized at individual excitatory synapses in the mammalian brain yet appear to subserve distinct functions. To address whether neuronal activity may differentially regulate the surface expression at synapses of two specific subtypes of ionotropic glutamate receptors we epitope-tagged an AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) receptor subunit (GluR1) and an NMDA (N-methyl-D-aspartate) receptor subunit (NR1) on their extracellular termini and expressed these proteins in cultured hippocampal neurons using recombinant adenoviruses. Both receptor subtypes were appropriately targeted to the synaptic plasma membrane as defined by colocalization with the synaptic vesicle protein synaptophysin. Increasing activity in the network of cultured cells by prolonged blockade of inhibitory synapses with the gamma-aminobutyric acid type A receptor antagonist picrotoxin caused an activity-dependent and NMDA receptor-dependent decrease in surface expression of GluR1, but not NR1, at synapses. Consistent with this observation identical treatment of noninfected cultures decreased the contribution of endogenous AMPA receptors to synaptic currents relative to endogenous NMDA receptors. These results indicate that neuronal activity can differentially regulate the surface expression of AMPA and NMDA receptors at individual synapses.

Adenoviridae↗
PubMed1990

Magnesium removal induces paroxysmal neuronal firing and NMDA receptor-mediated neuronal degeneration in cortical cultures.

Removal of extracellular Mg2+ triggered the onset of repetitive excitatory discharges in cultured murine cortical neurons, detected by recording with patch electrodes in the whole cell configuration. The discharges were suppressed by 100 microM D-2-amino-5-phosphonovalerate. Over the next 24-72 h substantial numbers of neurons, but not glia, degenerated, releasing lactate dehydrogenase to the bathing medium. The neuronal death induced by removal of extracellular Mg2+ could be attenuated by either 3 microM tetrodotoxin or 50 microM dextrorphan, and thus likely reflects excessive activation of N-methyl-D-aspartate receptors triggered by excitatory discharges. This Mg2+ removal model may be a useful model in which to study certain aspects of epileptic neocortical injury.

2-Amino-5-phosphonovalerate↗
PubMed1990

Acidosis reduces NMDA receptor activation, glutamate neurotoxicity, and oxygen-glucose deprivation neuronal injury in cortical cultures.

The acidosis which accompanies cerebral ischemia in vivo has been thought to contribute to subsequent neuronal injury. However, recent electrophysiological recordings from hippocampal neurons suggest that H+ can attenuate N-methyl-D-aspartate (NMDA) receptor-mediated cation influx, likely a key event in the pathogenesis of ischemic neuronal injury. Here we report that moderate extracellular acidosis (pH 6.5) markedly reduced the inward whole cell current induced by NMDA on cultured cortical neurons; at pH 6.1, kainate-induced current was additionally reduced. Furthermore, such acidosis reduced the cortical neuronal injury caused by toxic glutamate exposure, as well as the neuronal degeneration and accumulation of 45Ca2+ induced by combined oxygen and glucose deprivation. These findings raise the possibility that moderate acidosis may decrease cortical neuronal vulnerability to ischemic damage.

Acidosis↗
PubMed1990

Effect of zinc on NMDA receptor-mediated channel currents in cortical neurons.

Recent data have indicated that the divalent cation Zn2+ can selectively block central neuronal excitation mediated by N-methyl-D-aspartate (NMDA) receptors. The present experiments were conducted to determine the action of Zn2+ at the single-channel level. Outside-out membrane patches were prepared from cultured murine cortical neurons. Glutamate, 3 microM, in the presence of 5 microM glycine activated channels with a main conductance state of about 50 pS which were blocked in a voltage-dependent manner by Mg2+. Zn2+ appeared to have 2 effects on these NMDA receptor-activated channels. First, at concentrations as low as 1-10 microM, Zn2+ produced a concentration-dependent reduction in channel open probability, insensitive to membrane voltage between -60 and +40 mV; about 50% reduction in open probability was produced by 3 microM Zn2+. This reduction was mostly due to a decrease in opening frequency and only weakly mimicked by Mg2+. Second, at higher concentrations (10-100 microM) and negative membrane voltages, Zn2+ additionally produced an apparent reduction in single-channel amplitude, associated with an increase in channel noise, suggestive of a fast channel block. The amplitude reduction was voltage-dependent, with a delta of 0.51; amplitude distribution analysis suggested that this voltage dependence was primarily contributed by the "on" blocking rate constant, with little contribution from the "off" rate constant. The channel block produced by Zn2+ was faster than that of Mg2+, which at 100 microM and negative membrane voltages induces flickering of the NMDA receptor-activated channel without changing apparent channel amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Zinc and LTP.

Explore the source record for details and available documents.

Action Potentials↗
PubMed1989

Bicarbonate dependence of glutamate receptor activation by beta-N-methylamino-L-alanine: channel recording and study with related compounds.

beta-N-methylamino-L-alanine (BMAA) is a neurotoxic glutamate agonist possibly responsible for the neuronal degeneration found in the Guam amyotrophic lateral sclerosis-Parkinsonism-dementia complex. The basis for glutamate receptor activation by BMAA has been unclear, as BMAA lacks the omega electronegative moiety characteristic of other excitatory amino acids. We recently reported that the neuroexcitatory and neurotoxic effects of BMAA depend strongly on the presence of bicarbonate ions and proposed that an interaction between bicarbonate and the beta amino group of BMAA produces a molecular configuration appropriate for activating glutamate receptors. We now report that bicarbonate potentiates the ability of BMAA to open NMDA receptor-activated channels in isolated membrane patches. Furthermore, the neurotoxic and neuroexcitatory effects of two structural analogs of BMAA, DL-2,4-diaminobutyrate and DL-2,3-diaminopropionate, were also potentiated by bicarbonate. These findings support the bicarbonate cofactor hypothesis for BMAA action and provide direct evidence that it may be generalizable to certain other compounds.

Amino Acids, Diamino↗
PubMed1987

High-conductance K+ channel in apical membranes of principal cells cultured from rabbit renal cortical collecting duct anlagen.

Using the patch clamp technique, one type of K+ channel was identified in the apical cell membrane of cultured principal cells of rabbit renal collecting ducts in the cell-attached or excised-patch configuration. The channel was highly selective for K+ over Na+ (typically 30-70-fold) and had a conductance of 180, SD +/- 39 pS (n = 6), referred to a situation of 140 mmolar K+-Ringer solution present on either surface of the patch membrane. Channel activity was completely blocked by Ba2+ (5 mmol/l) and partially inhibited by Na+. The latter was evidenced by a deviation from Goldman rectification at high cytoplasm-positive membrane potentials, which was observed when Na+ competed with K+ for channel entrance from the cytoplasmic surface. Channel open probability depended strongly on membrane voltage and cytoplasmic Ca2+ concentration. Open-close kinetics exhibited double exponential behaviour, with a strong voltage dependence of the slow open time constant. Infrequently also a substate conductance level was identified. The voltage and calcium dependence suggest that the channel plays a role in adjusting K+ secretion to Na+ absorption in the fine regulation of cation excretion in renal collecting ducts.

Animals↗
PubMedDate not supplied

Cation channels in the apical membrane of collecting duct principal cell epithelium in culture.

The apical cell membrane of cultured monolayers of collecting duct principal cells was investigated with the patch-clamp technique to study single ion channels. A broad spectrum of channel events was observed which complicated the analysis. Although principal cells absorb mainly Na+ ions and although most patches must have contained an Na+ conductance as evidenced by asymmetric clamp currents in the presence of amiloride, single Na+ channel events could not be identified with certainty, possibly because single-channel conductance was too low (less than or equal to 5 pS). Instead, non-selective cation channels of 21.2 +/- 4.0 pS were frequently observed. They were impermeable to choline and anions but did not discriminate between Na+ and K+. These channels, however, do not appear to participate in active Na+ absorption. Different types of K+ channels were observed: a high-conductance Ca2(+)-activated K+ channel and a bursting low-conductance K+ channel. Since the former channel has been denied a role in K+ secretion/absorption in native collecting ducts, the latter might be involved. In addition three types of Cl- channels have been observed which will be described separately. At least one of those, a 30-pS outwardly rectifying Cl- channel appears to allow small amounts of Cl- ions to be absorbed across principal cells.

Animals↗