The neuroprotection conferred by activating the mitochondrial ATP-sensitive K(+) channel is mediated by inhibiting the mitochondrial permeability transition pore.

摘要

In order to further explore the mechanisms by which activation of mitochondrial ATP-sensitive potassium channels (mitoK(ATP)) confers neuroprotection, we investigated the role of the mitochondrial permeability transition pore (MPTP) in in vivo and in vitro models. Adult male Sprague-Dawley rats were exposed to 90min of middle cerebral artery occlusion (MCAO) followed by reperfusion for 22h, when neurological scores and infarct volumes were evaluated. Activating mitoK(ATP) by infusion of 2mmol/L diazoxide into the ventricles 20min before MCAO or inhibiting the MPTP by infusion of 1mumol/L cyclosporin A 15min before reperfusion significantly increased functional score and reduced infarction volume. Subsequent intracerebroventricular infusion of 2mmol/L atractyloside, the MPTP opener, 10min before reperfusion significantly attenuated the neuroprotective effects of diazoxide and cyclosporin A. The swelling of mitochondria isolated from brain was evaluated by spectrophotometry and served as a measure of MPTP opening. In isolated mitochondria, 100mumol/L atractyloside attenuated the decrease of mitochondrial swelling induced by 30mumol/L diazoxide or cyclosporin A (0.5 or 1mumol/L). Furthermore, 100mumol/L diazoxide or 1mumol/L cyclosporin A both attenuated the fluorescence intensity in isolated mitochondria loaded with rhod-2 acetoxymethylester, and 100mumol/L atractyloside abolished the effects of diazoxide and cyclosporin A. These results suggest that activation of mitoK(ATP) protects the brain against injury, and this is probably mediated by attenuating mitochondrial Ca(2+) overload and thus inhibiting MPTP opening during brain ischemia and reperfusion.