Kir6.2 limits Ca overload and mitochondrial oscillations of ventricular myocytes in response to metabolic stress

Storey NM, Stratton RC, Rainbow RD, Standen NB, Lodwick D. Kir6.2 limits Ca overload and mitochondrial oscillations of ventricular myocytes in response to metabolic stress. Am J Physiol Heart Circ Physiol 305: H1508–H1518, 2013. First published September 6, 2013; doi:10.1152/ajpheart.00540.2013.—ATP-sensitive K (KATP) channels are abundant membrane proteins in cardiac myocytes that are directly gated by intracellular ATP and form a signaling complex with metabolic enzymes, such as creatine kinase. KATP channels are known to be essential for adaption to cardiac stress, such as ischemia; however, how all the molecular components of the stress response interact is not fully understood. We examined the effects of decreasing the KATP current density on Ca and mitochondrial homeostasis and ischemic preconditioning. Acute knockdown of the pore-forming subunit, Kir6.2, was achieved using adenoviral delivery of short hairpin RNA targeted to Kir6.2. The acute nature of the knockdown of Kir6.2 accurately shows the effects of Kir6.2 depletion without any compensatory effects that may arise in transgenic studies. We also investigated the effect of reducing the KATP current while maintaining KATP channel protein in the sarcolemmal membrane using a nonconducting Kir6.2 construct. Only 50% KATP current remained after Kir6.2 knockdown, yet there were profound effects on myocyte responses to metabolic stress. Kir6.2 was essential for cardiac myocyte Ca homeostasis under both baseline conditions before any metabolic stress and after metabolic stress. Expression of nonconducting Kir6.2 also resulted in increased Ca overload, showing the importance of K conductance in the protective response. Both ischemic preconditioning and protection during ischemia were lost when Kir6.2 was knocked down. KATP current density was also important for the mitochondrial membrane potential at rest and prevented mitochondrial membrane potential oscillations during oxidative stress. KATP channel density is important for adaption to metabolic stress.