Mitochondrial ATP‐sensitive K⁺ channels regulate NMDAR activity in the cortex of the anoxic western painted turtle

Abstract

] c 8.9 ± 0.7% and 3.8 ± 0.3%, while decreasing normoxic whole-cell NMDAR currents by 41.1 ± 6.7% and 55.4 ± 10.2%, respectively. These changes were also blocked by 5HD or glibenclamide, BAPTA, or spermine. Blockade of mitochondrial Ca 2+ -uptake decreased normoxic NMDAR currents 47.0 ± 3.1% and this change was blocked by BAPTA but not by 5HD. Taken together, these data suggest mK ATP channel activation in the anoxic turtle cortex uncouples mitochondria and reduces mitochondrial Ca 2+ uptake via the uniporter, subsequently increasing [Ca 2+ ] c and decreasing NMDAR activity.

Anoxia-mediated calcium release through the mitochondrial permeability transition pore silences NMDA receptor currents in turtle neurons

“…2A,D). This agrees with previous studies investigating anoxia-mediated NMDAR channel arrest (Shin and Buck, 2003;Pamenter et al, 2008b). Anoxic conditions in the recording chamber after 30 min of anoxic saline perfusion were confirmed using an oxygen electrode (data not shown).…”

“…This increase in Ca 2+ -induced fluorescence was still observed in the absence of extracellular Ca 2+ (17.79±3.52%, N=4, P<0.05; Fig. 4A,D), which, in accordance with previous observations (Pamenter et al, 2008b), demonstrates that the increased [Ca 2+ ] during anoxia is caused by release from an intracellular source. To investigate whether this increase in Ca 2+ is due to release through the mPTP, opening of the mPTP was stimulated with atractyloside during normoxic conditions.…”

“…These changes occur in a calcium-dependent manner: [Ca 2+ ] i levels increase by 35% following the onset of anoxia (Bickler et al, 2000) and inclusion of the Ca 2+ chelator BAPTA [1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid] in the pipette solution of electrodes during wholecell patch clamp experiments abolished the anoxia-mediated reduction in NMDAR currents (Pamenter et al, 2008b). The anoxiamediated rise in Ca 2+ occurs in the absence of extracellular Ca ] i (Pamenter et al, 2008b). It is of interest to understand the mechanism of how a reduction of oxygen is transduced into a signal for mitochondrial Ca 2+ release that leads to NMDAR silencing.…”

“…In addition to maintaining extracellular [glutamate] at basal levels through 5 h of anoxia (Thompson et al, 2007), turtle neurons regulate NMDAR activity through a reduction in channel open time; open probability is reduced by 65% after 60 min of anoxia ) and whole-cell NMDAR currents are reduced by 45-65% after 40 min of anoxia (Pamenter et al, 2008b;Shin and Buck, 2003;Bickler et al, 2000). These changes occur in a calcium-dependent manner: [Ca 2+ ] i levels increase by 35% following the onset of anoxia (Bickler et al, 2000) and inclusion of the Ca 2+ chelator BAPTA [1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid] in the pipette solution of electrodes during wholecell patch clamp experiments abolished the anoxia-mediated reduction in NMDAR currents (Pamenter et al, 2008b).…”

Mitochondrial responses to prolonged anoxia in brain of red-eared slider turtles

“…mK ATP channel activation increases mitochondrial membrane permeability to K þ , and the resulting K þ flux through these channels must be opposed by the activity of H þ -fuelled antiporters. This futile K þ cycle thereby mildly uncouples the H þ gradient from ATP production but initiates glutamatergic channel arrest [13], a key neuroprotective mechanism against anoxia in turtle brain. Channel arrest persists for at least the first three weeks of anoxic exposure in turtles [14]; mild uncoupling of the mitochondrial H þ gradient due to mK ATP channel activation would explain the observed shift.…”