J Physiol Volume 586, Number 4, 1043-1058, February 15, 2008 DOI: 10.1113/jphysiol.2007.142380
Mitochondrial ATP-sensitive K+ channels regulate NMDAR activity in the cortex of the anoxic western painted turtle
Matthew Edward Pamenter1,2,
Damian Seung-Ho Shin3,
Mohan Cooray1 and
Leslie Thomas Buck1,2
1 Department of Cellular and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5
2 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3G5
3 Division of Fundamental Neurobiology, Toronto Western Research Institute, Toronto, ON, Canada M5T 2S8
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 ([Ca2+]c) within a narrow range during anoxia. In mammalian ischaemic models, activation of mitochondrial ATP-sensitive K+ (mKATP) channels partially uncouples mitochondria resulting in a moderate increase in [Ca2+]c and neuroprotection. The aim of this study was to determine the role of mKATP channels in anoxic turtle NMDAR regulation and if mitochondrial uncoupling and [Ca2+]c changes underlie this regulation. In isolated mitochondria, the KATP 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 mKATP antagonist 5-hydroxydecanoic acid (5HD). During anoxia, [Ca2+]c increased 9.3 ± 0.3% and NMDAR currents decreased 48.9 ± 4.1%. These changes were abolished by KATP channel blockade with 5HD or glibenclamide, Ca2+c chelation with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or by activation of the mitochondrial Ca2+ uniporter with spermine. Similar to anoxia, diazoxide or levcromakalim increased [Ca2+]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 Ca2+-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 mKATP channel activation in the anoxic turtle cortex uncouples mitochondria and reduces mitochondrial Ca2+ uptake via the uniporter, subsequently increasing [Ca2+]c and decreasing NMDAR activity.
(Received 2 August 2007;
accepted after revision 12 December 2007;
first published online 13 December 2007)
Corresponding author L.T. Buck: University of Toronto, Dept. of Cellular and Systems Biology, 25 Harbord Street, Toronto, ON M5S 3G5. buckl{at}zoo.utoronto.ca
Copyright © 2008 The Physiological Society.
