Pharmacology and Toxicology

Mitochondria constitute the core of cellular energy metabolism as the site of the greatest ATP production. In addition, they play an important role in regulating ionic homeostasis of the cell. It has been suggested that mitochondrial dysfunction may be the major cause for tissue injury during cardiac ischemia and reperfusion. Exposure of the heart to volatile anesthetics like isoflurane before or after an ischemic event helps to maintain cellular and mitochondrial function both in the whole heart and in isolated mitochondria. One of my research interests revolves around the role of mitochondria in the protection of the heart from ischemia and stress. We use physiological, pharmacological and molecular techniques as well as proteomics to demonstrate quantifiable alterations in protein expression and mitochondrial bioenergetics after exposure to isoflurane or xenon. We plan to apply our findings to target potentially protective proteins to mitochondria by overexpression, thereby increasing the cardiomyocytes' resistance against oxidative stress.

Another component important in protection of the heart from stress are ion channels. A case in point are ATP-sensitive potassium channels (K_ATP) that are expressed in the sarcolemmal membrane and couple the metabolic state of the cell with the membrane excitability. They serve as an important component in the cardioprotective phenomenon of ischemic or pharmacological preconditioning. We are dissecting the molecular mechanisms by which volatile anesthetics modulate this channel. To investigate the mechanism of anesthetic-channel interaction, we are evaluating the effects of pH and isoflurane on the sarcK_ATP channel subunits, the channel pore inward rectifier Kir6.2 and the regulatory sulfonylurea receptor SUR2A in a heterologous expression system, applying site-directed mutagenesis.

Channels resembling the sarcolemmal K_ATP channel have been also found in mitochondria and we are interested in investigating their molecular identity and function. While there is an increasing amount of data that, based upon the pharmacological targeting of putative mitochondrial K⁺-channels, support the cardioprotective efficacy of mitochondrial K⁺ influx, direct evidence for K⁺ flux and its protective mechanism is largely missing. In addition, the identity and even the existence of mitoK_ATP channels are questioned. Therefore, we are assessing the protective mechanism of K⁺ flux independently from pharmacological regulators by targeting the inward rectifier potassium channel Kir6.2 to mitochondria of cardiomyocytes in order to test the hypothesis that increased K⁺ influx to mitochondria confers protection against metabolic stress. Additionally, we compared the pharmacological profile of Kir6.2 expressed in mitochondria with previously published reports on the mitoK_ATP channel, and analyze the Ca²⁺ handling and ROS production from these modified cells.

Bienengraeber, M, Olson TM, Selivanov VA, Kathmann EC, O'Coclain F, Gao F, Karger AB, Ballew JD, Hodgson, DM, Zingman LV, Pang Y-P, Alekseev AE, Terzic A: SUR2A mutations identified in human dilated cardiomyopathy disrupt catalytic KATP channel gating.  Nat Genet 36:382-387, 2004.

Chiari PC, Bienengraeber MW, Pagel PS, Krolikowski JG, Kersten JR, Warltier DC: Isoflurane protects against myocardial infarction during early reperfusion by activation of phosphatidylinositol-3-kinase signal transduction: Evidence for anesthetic-induced postconditioning in rabbits. Anesthesiology 102:102-109, 2005.

Chiari PC, Bienengraeber MW, Weihrauch D, Krolikowski JG, Kersten JR, Warltier DC, Pagel PS:  Role of endothelial nitric oxide synthase as a trigger and mediator of isoflurane-induced delayed preconditioning in rabbit myocardium.  Anesthesiology 103:74-83, 2005.

Bienengraeber MW, Weihrauch D, Kersten JR, Pagel PS, Warltier DC:  Cardioprotection by volatile anesthetics.  Vascul Pharmacol 42:243-252, 2005.

Weihrauch D, Krolikowski JG, Bienengraeber MW, Kersten JR, Warltier DC, Pagel PS:  Morphine enhances isoflurane-induced postconditioning against myocardial infarction:  Role of phosphatidylinositol-3-kinase and opioid receptors in rabbits.  Anesth Analg 101(4):942-9,.2005.