Regulation of AMPA receptor currents by 3 mitochondrial ATP sensitive K + channels in anoxic 4 turtle neurons

24 Mammalian neurons rapidly undergo excitotoxic cell death during anoxia, while neurons 25 from the anoxia-tolerant painted turtle survive without oxygen for hours and offer a unique 26 model to study mechanisms to reduce the severity of cerebral stroke. An anoxia-mediated 27 decrease in whole-cell NMDA and AMPA receptor currents are an important part of the turtle’s 28 natural defence. Here we investigate the role of mitochondrial KATP channels in the regulation of 29 AMPAR. Whole-cell AMPAR currents were stable over 90 min of normoxic recording; 30 however, anoxia resulted in a 52% decrease in AMPAR currents. Pharmacological activation of 31 mKATP channels with diazoxide or levcromakalim resulted in a 46% decrease in normoxic 32 AMPAR currents, and the decrease was abolished with application of the antagonists 533 hydroxydecanoic acid and glibenclamide, while mKATP antagonists blocked the anoxia-mediated 34 decrease. Mitochondrial KCa channel modulators responded similarly. The Ca-uniporter 35 antagonist ruthenium red reduced AMPAR currents by 38% and was blocked with the agonist 36 spermine. The calcium chelator BAPTA in the recording electrode during anoxia or diazoxide 37 perfusion also abolished the reduction in AMPAR currents. We conclude that the mKATP channel 38 is involved in the anoxia-mediated down-regulation of AMPAR activity during anoxia and that it 39 is a common mechanism to reduce glutamatergic excitability. 40