title: Mitochondrial ATP-sensitive K+ channels regulate NMDAR activity in the cortex of the anoxic western painted turtle.
abstract: Hypoxic mammalian neurons undergo excitotoxic cell death, whereas painted turtle neurons survive prolonged anoxia without apparent injury. Anoxic survival is possibly mediated by a decrease in N-methyl-d-aspartate receptor (NMDAR) activity and maintenance of cellular calcium concentrations ([Ca(2+)](c)) within a narrow range during anoxia. In mammalian ischaemic models, activation of mitochondrial ATP-sensitive K(+) (mK(ATP)) channels partially uncouples mitochondria resulting in a moderate increase in [Ca(2+)](c) and neuroprotection. The aim of this study was to determine the role of mK(ATP) channels in anoxic turtle NMDAR regulation and if mitochondrial uncoupling and [Ca(2+)](c) changes underlie this regulation. In isolated mitochondria, the K(ATP) channel activators diazoxide and levcromakalim increased mitochondrial respiration and decreased ATP production rates, indicating mitochondria were 'mildly' uncoupled by 10-20%. These changes were blocked by the mK(ATP) antagonist 5-hydroxydecanoic acid (5HD). During anoxia, [Ca(2+)](c) increased 9.3 +/- 0.3% and NMDAR currents decreased 48.9 +/- 4.1%. These changes were abolished by K(ATP) channel blockade with 5HD or glibenclamide, Ca(2+)(c) chelation with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or by activation of the mitochondrial Ca(2+) uniporter with spermine. Similar to anoxia, diazoxide or levcromakalim increased [Ca(2+)](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.
authors: Department of Cellular and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5.
authors: Matthew Edward
authors: ME
authors: Pamenter
authors: Damian Seung-Ho
authors: DS
authors: Shin
authors: Mohan
authors: M
authors: Cooray
authors: Leslie Thomas
authors: LT
authors: Buck
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D019806:Cromakalim / Q000494:pharmacology; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006880:Hydroxy Acids / Q000494:pharmacology; D000860:Hypoxia / Q000503:physiopathology; D054086:KATP Channels / Q000502:physiology*; D008929:Mitochondria, Heart / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D014426:Turtles / Q000502:physiology*
chemical_list: D003652:Decanoic Acids; D006880:Hydroxy Acids; D054086:KATP Channels; D026902:Potassium Channel Blockers; D016194:Receptors, N-Methyl-D-Aspartate; D019806:Cromakalim; C052853:5-hydroxydecanoic acid; D000255:Adenosine Triphosphate; D003981:Diazoxide; D005905:Glyburide; D002118:Calcium