Identification and Properties of a Novel Intracellular (Mitochondrial) ATP-sensitive Potassium Channel in Brain

Abstract

Protection of heart against ischemia-reperfusion injury by ischemic preconditioning and K ATP channel openers is known to involve the mitochondrial ATPsensitive K ؉ channel (mitoK ATP ). Brain is also protected by ischemic preconditioning and K ATP channel openers, and it has been suggested that mitoK ATP may also play a key role in brain protection. However, it is not known whether mitoK ATP exists in brain mitochondria, and, if so, whether its properties are similar to or different from those of heart mitoK ATP . We report partial purification and reconstitution of a new mitoK ATP from rat brain mitochondria. We measured K ؉ flux in proteoliposomes and found that brain mitoK ATP is regulated by the same ligands as those that regulate mitoK ATP from heart and liver. We also examined the effects of opening and closing mitoK ATP on brain mitochondrial respiration, and we estimated the amount of mitoK ATP by means of green fluorescence probe BODIPY-FL-glyburide labeling of the sulfonylurea receptor of mitoK ATP from brain and liver. Three independent methods indicate that brain mitochondria contain six to seven times more mitoK ATP per milligram of mitochondrial protein than liver or heart.

Neuroprotective role of ATP-sensitive potassium channels in cerebral ischemia

“…Immunohistochemical studies showed that Kir6.2 subunits are mainly located in the somata and dendrites of the central neurons [92,93,96] . Mitochondrial K ATP channels are also found in the rat brain, and the expression level of Kir6.1 (per milligram of mitochondrial protein) is six to seven times higher than that in the heart and liver [12] . Radioligand binding studies showed that regional expression of K ATP channels in the brain showed different affinities to sulfonylureas [97] .…”

“…Kir6.1-based channels have a smaller unitary conductance than Kir6.2 subtype channels [27] . Kir6.2 subunits are found in plasmalemmal membranes (cell surface membranes) [12,20,27,29,32] . Most functional K ATP channels contain the Kir6.2 subunit; thus, the heterogeneity observed between different K ATP channels mainly arises from the differential expression of the SUR regulatory subunits.…”

“…Kir6.2 was cloned from a human genomic library and shares 96% amino acid identity with mouse and rat Kir6.2 [30] . Kir6.1 genes (KCNJ8) are mainly expressed in the mito chondria [12,31,32] . Two SUR subunits, SUR1 and SUR2, have been identified as the regulatory subunits of K ATP channels [33] .…”

Adenosine A1 Receptor Antagonist and Mitochondrial ATP-Sensitive Potassium Channel Blocker Attenuate the Tolerance to Focal Cerebral Ischemia in Rats

“…In the brain, however, the role of mitochondrial K ATP channels in ischemic tolerance remains to be elucidated, although inhibition of preconditioning-induced protection by a nonspecific antagonist acting on both surface and mitochondrial K ATP channels has been reported in global ischemia (Heurteaux et al, 1995). Recently, a mitochondrial K ATP channel proteins were partially purified from rat brain mitochondria and exhibited ligand-binding properties similar to those of heart mitochondrial K ATP channels (Bajgar et al, 2001). The amount of mitochondrial K ATP channels in the brain was reported to be much higher than in the heart (Bajgar et al, 2001), suggesting the possibility that mitochondrial K ATP channels play an important role in neural function.…”

Cellular Caspases: New Targets for the Action of Pharmacological Agents

“…Pore opening can be stimulated by inorganic phosphate, caspases, SH-reagents, cell exhaustion by reduced glutathione, formation of active forms of oxygen, uncoupling of oxidative phosphorylation, rise in Ca 2+ content in the cytoplasm, effect of ceramide, depletion of the mitochondrial ATP pool, etc. [24,27,28].…”