Single channel studies of the ATP-regulated potassium channel in brain mitochondria Katarzyna Choma & Piotr Bednarczyk & Izabela Koszela-Piotrowska & Bogusz Kulawiak & Alexei Kudin & Wolfram S. Kunz & Krzysztof Dolowy & Adam Szewczyk Received: 15 June 2009 / Accepted: 21 July 2009 / Published online: 15 September 2009 # Springer Science + Business Media, LLC 2009 Abstract Mitochondrial potassium channels in the brain have been suggested to have an important role in neuro- protection. The single channel activity of mitochondrial potassium channels was measured after reconstitution of the purified inner membrane from rat brain mitochondria into a planar lipid bilayer. In addition to a large conductance potassium channel that was described previously, we identified a potassium channel that has a mean conductance of 219 ± 15 pS. The activity of this channel was inhibited by ATP/Mg 2+ and activated by the potassium channel opener BMS191095. Channel activity was not influenced either by 5-hydroxydecanoic acid, an inhibitor of mito- chondrial ATP-regulated potassium channels, or by the plasma membrane ATP-regulated potassium channel blocker HMR1098. Likewise, this mitochondrial potassium channel was unaffected by the large conductance potassium channel inhibitor iberiotoxin or by the voltage-dependent potassium channel inhibitor margatoxin. The amplitude of the con- ductance was lowered by magnesium ions, but the opening ability was unaffected. Immunological studies identified the Kir6.1 channel subunit in the inner membrane from rat brain mitochondria. Taken together, our results demonstrate for the first time the single channel activity and properties of an ATP-regulated potassium channel from rat brain mitochondria. Keywords Mitochondria . Potassium channel . ATP . Potassium channel openers . Rat brain . Planar lipid membrane Introduction Four different types of potassium channels have been described in the inner mitochondrial membrane: an ATP- regulated potassium channel (the mitoK ATP channel), a large Ca 2+ -activated potassium channel (the mitoBK Ca channel), a voltage-gated potassium channel (the mitoKv1.3 channel) and twin-pore TASK-3 potassium channels (Szewczyk and Wojtczak 2002; Szewczyk et al. 1996, 2006, 2009; Zoratti et al. 2008). It has been postulated that mitochondrial potassi- um channels play a pivotal role in cardio- and neuro- protection (O’Rourke 2004; Ardehali 2005; Costa and Garlid 2009). Although the details of this cytoprotective mecha- nism have not yet been fully elucidated, it is believed that an increase in the K + flux (via mitochondrial potassium channels) into the mitochondrial matrix, followed by changes in mitochondrial volume or the generation of reactive oxygen species (ROS), may play a triggering role (Kowaltowski et al. 2001; Kis et al. 2003; Busija et al. 2004; Facundo et al. 2005; Kulawiak et al. 2008). Increased understanding of the properties of the mitoK ATP channels Katarzyna Choma and Piotr Bednarczyk contributed equally to this work. K. Choma : P. Bednarczyk : K. Dolowy Department of Biophysics, Warsaw University of Life Sciences SGGW, 159 Nowoursynowska St., 02-776 Warsaw, Poland K. Choma : P. Bednarczyk : I. Koszela-Piotrowska : B. Kulawiak : A. Szewczyk (*) Laboratory of Intracellular Ion Channels, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093 Warsaw, Poland e-mail: adam@nencki.gov.pl A. Kudin : W. S. Kunz Department of Epileptology, University Bonn Medical Center, Sigmund-Freud-Str. 25, 53105 Bonn, Germany J Bioenerg Biomembr (2009) 41:323–334 DOI 10.1007/s10863-009-9233-7