Heptanol triggers cardioprotection via mitochondrial mechanisms and mitochondrial potassium channel opening in rat hearts D. Johansen, 1 E. Sanden, 1 M. Hagve, 1 X. Chu, 1 R. Sundset 1,2 and K. Ytrehus 1 1 Cardiovascular Research Group, Department of Medical Biology and Department of Clinical Medicine, Faculty of Health Sciences, University of Tromsø, Tromsø, Norway 2 Section of Nuclear Medicine, University Hospital North Norway, Tromsø, Norway Received 1 July 2010, revision requested 10 August 2010, final revision received 1 November 2010, accepted 3 November 2010 Correspondence: D. Johansen, Cardiovascular Research Group, Faculty of Health Sciences, University of Tromsø, Tromsø 9037, Norway. E-mail: david.johansen@uit.no Abstract Aim: To investigate mechanisms behind heptanol (Hp)-induced infarct size reduction and in particular if protection by pre-treatment with Hp is trig- gered through mitochondrial mechanisms. Methods: Langendorff perfused rat hearts, isolated mitochondria and iso- lated myocytes were used. Infarct size, mitochondrial respiration, time to mitochondrial permeability transition pore (MPTP) opening and AKT and glycogen synthase kinase 3 beta (GSK-3b) phosphorylation were examined. Results: Pre-treatment with Hp reduced infarct size from 29.7 Æ 3.4% to 12.6 Æ 2.1%. Mitochondrial potassium channel blockers 5-hydroxy deca- noic acid (5HD) blocking mitoK ATP and paxilline (PAX) blocking mitoK Ca abolished cardioprotective effect of Hp (Hp + 5HD 36.7 Æ 2.9% and Hp + PAX 40.2 Æ 2.8%). Hp significantly reduced respiratory control ratio in both subsarcolemmal and interfibrillar mitochondria in a dose-dependent manner (0.5–5.0 mm). The ADP oxygen ratio was also significantly reduced by Hp (2 mm). Laser scanning confocal microscopy of tetramethylrhod- amine-loaded isolated rat myocytes using line scan mode showed that Hp increased time to MPTP opening. Western blot analysis showed that pre- treatment with Hp increased phosphorylation of AKT and GSK-3b before ischaemia and after 30 min of global ischaemia. Conclusion: Pre-treatment with Hp protects the heart against ischaemia- reperfusion injury. This protection is most likely mediated via mitochondrial mechanisms which initiate a signalling cascade that converges on inhibition of opening of MPTP. Keywords cardioprotection, gap junction, heptanol, ischaemia, mitochon- dria, potassium channels. The heart, as well as other organs and cell systems, have endogenous mechanisms which when triggered confer protection against ischaemic cell death (Murry et al. 1986, Kitagawa et al. 1990). Mitochondria have for a long time been suggested to harbour the end-effector of ischaemic preconditioning (IPC) (Crompton & Costi 1988, Hausenloy et al. 2002). Many mechanisms have been proposed by which mitochondria can participate in IPC and several of them include an increase in potassium (K + ) influx into the mitochondrial matrix. Munch- Ellingsen et al. (2000) showed that by blocking mitoK ATP channels the effect of IPC was abolished. Cao et al. (2005) showed that calcium-activated potas- sium channels in mitochondria was important in IPC. By blocking mitoK Ca channels they abolished the cardio- protective effects of IPC. It is known that mitochondrial permeability transition pores (MPTP) open at reperfu- sion after prolonged ischaemia, and this is followed by Acta Physiol 2011, 201, 435–444 Ó 2010 The Authors Acta Physiologica Ó 2010 Scandinavian Physiological Society, doi: 10.1111/j.1748-1716.2010.02221.x 435