Mitochondrial permeability transition dynamics: an indicator of mitochondrial potassium channel opener

Mitochondrial permeability transition (MPT) is an intracellular event that is closely related to apoptosis and necrosis. However, whether this process underlies the recently reported neuroprotective potency of mitochondrial potassium channel openers applied in vivo remains uncertain. This study aims to clarify this issue by determining the effects of potassium channel openers on MPT dynamics in vitro along with their in vivo effects. Male Sprague-Dawley rats were subjected to middle cerebral artery occlusion (MCAO) for 90 min, followed by reperfusion. 30μl of diazoxide, an opener of the mitochondrial adenosine triphosphate-sensitive K⁺channel (mitoKATP), or NS1619, an opener of the mitochondrial Ca²⁺-activated potassium channel (mitoKCa) (2 mM and 0.1 mM respectively), was infused into the right lateral cerebral ventricle 15 min before the induction of ischemia. Neurological scores were assessed 24 h after MCAO and then infarct area was determined by standard 2,3,5-triphenyltetrazolium chloride staining techniques. To further clarify the capacity of diazoxide and NS1619 to protect mitochondria from Ca²⁺-induced MPT, we isolated brain-derived non-synaptosomal mitochondria and evaluated the effects of diazoxide and NS1619 on Ca²⁺-induced MPT dynamics through measurement of spectrophotometric alterations in light scattering at 520 nm. Neurological scores and infarct size were improved in animals pretreated with diazoxide and NS1619. In isolated mitochondria, MPT was readily induced by 200 μM Ca²⁺and was effectively inhibited by diazoxide and NS1619. The specific MPT pore opener atractyloside abolished the inhibitory effects. According to time-constant analysis, MPT dynamics was in accordance with the neuroprotective effects of channel openers in vivo.