Institute of Anesthesiology and Pharmacology

University of Zurich

Differential effects of anaesthetics on mitochondrial K_ATP channel activity and cardiomyocyte protection. Using autofluorescence in live cell imaging microscopy and a simulated model of ischaemia, we presented evidence that volatile anaesthetics (VAs) mediate their protection in cardiomyocytes by selectively priming the mitochondrial K_ATP channels through multiple triggering PKC-coupled signaling pathways. These observations provided important new insight into the mechanisms of volatile anaesthetic-induced preconditioning. Many anaesthetics have profound effects on mitochondrial membranes at concentrations as low as those known to produce general anaesthesia, and can affect lipid-protein interactions or induce conformational changes in proteins. It therefore appears likely that other anaesthetics than VAs may also affect mitochondrial K_ATP channel activity and thereby modulate myocyte protection. Although inhibitory effects of some intravenous anaesthetics on sarcolemmal K_ATP channels were previously reported using the patch-clamp method, no data was available regarding the effects of intravenous anaesthetics on mitochondrial K_ATP channel activity. It was therefore our aim to investigate whether the finding of the modulatory effect by VAs on the mitochondrial K_ATP channel activity also pertains to other commonly employed intravenous anaesthetics. Live cell microscopy was used to visualize and measure autofluorescence of flavoproteins, a direct reporter of mitochondrial K_ATP channel activity, in response to the direct and highly selective mitochondrial K_ATP channel opener diazoxide, or to diazoxide following exposure to various intravenous anaesthetics commonly used in clinical and experimental medicine. A cellular model of ischaemia with subsequent hypoosmolar trypan blue staining served to confirm the effects of the anaesthetics on mitochondrial K_ATP channels with respect to myocyte viability. Diazoxide-induced mitochondrial K_ATP channel opening was significantly inhibited by the anaesthetics R-ketamine, and the barbiturates thiopental and pentobarbital. Conversely, urethane, 2,2,2-trichloroethanol (main metabolite of a-chloralose and chloral hydrate), and the opioid fentanyl potentiated the channel-opening effect of diazoxide, which was abrogated by coadministration of chelerythrine, a specific protein kinase C (PKC) inhibitor. S-ketamine, xylazine, midazolam, propofol, and etomidate did not affect mitochondrial K_ATP channel activity. The significance of these modulatory effects of the anaesthetics on mitochondrial K_ATP channel activity was substantiated in a cellular model of simulated ischaemia, where diazoxide-induced cell protection was mitigated by R-ketamine and barbiturates, while urethane, 2,2,2-trichloroethanol, fentanyl potentiated myocyte protection. These results suggest distinctive actions of individual intravenous anaesthetics on the mitochondrial K_ATP channels, and provided evidence that the choice of background anaesthesia may play a role in cardiac protection under experimental and clinical conditions.

Preconditioning by Sevoflurane Decreases Biochemical Markers for Myocardial and Renal Dysfunction in Coronary Artery Bypass Graft Surgery: A Double-blinded Placebo-controlled Multicenter Study. Preconditioning by VAs is a promising therapeutic strategy to render myocardial tissue resistant to perioperative ischaemia. It was hypothesized that sevoflurane preconditioning would decrease postoperative release of brain natriuretic peptide (NT-proBNP), a biochemical marker for myocardial dysfunction (21). In addition, several variables associated with the protective effects of preconditioning were evaluated. Seventy-two patients scheduled for coronary artery bypass graft (CABG) surgery under cardioplegic arrest were randomly assigned to preconditioning during the first 10 minutes of complete cardiopulmonary bypass with either placebo (oxygen in air mixture only) or sevoflurane 4 vol% (2 minimum alveolar concentration). No other VAs were administered at any time during the study. Intravenous propofol was used as background anaesthesia. Biochemical markers of myocardial dysfunction and injury (NT-proBNP, creatine-kinase MB (CK-MB) activity, cardiac troponin T (cTnT)), and renal dysfunction (cystatin C (CysC)) were determined. Holter electrocardiography was recorded perioperatively. Translocation of protein kinase C (PKC) was assessed by immunohistochemistry in atrial samples. Sevoflurane preconditioning significantly decreased postoperative release of NT-proBNP, a sensitive biochemical marker of myocardial contractile dysfunction. Pronounced PKC d and e translocation was observed in sevoflurane-preconditioned myocardium. In addition, postoperative CysC plasma levels increased significantly less in sevoflurane-preconditioned patients. No differences between groups were found for perioperative ST-segment changes, arrhythmias, or CK-MB and cTnT release. Sevoflurane preconditioning preserves myocardial and renal function as assessed by biochemical markers in patients undergoing CABG surgery under cardioplegic arrest. The 1-year follow-up of these study patients revealed a significant difference with respect to CABG reocclusion and episodes of newly developed congestive heart failure in favor of the sevoflurane-preconditioned patients. In the placebo-group 6 patients had adverse cardiac events (3 with CABG reocclusion, 3 with episodes of congestive heart failure), while in the sevoflurane-group only 1 patient experienced congestive heart failure (log rank test p-value=0.038).

Suggested reading

Basic mechanisms of preconditioning

Zaugg M, Lucchinetti E, Uecker M, Pasch T, Schaub MC. REVIEW Part I. Anaesthetics and cardiac preconditioning: signalling and cytoprotective mechanisms. Br J Anaesth 2003;91:551-565.

Uecker M, da Silva R, Grampp T, Pasch T, Schaub MC, Zaugg M. Translocation of protein kinase C isoforms to subcellular targets in ischemic and anesthetic preconditioning. Anesthesiology 2003;99:138-147.

da Silva R, Grampp T, Pasch T, Schaub MC, Zaugg M. Differential activation of mitogen-activated protein kinases in ischemic and anesthetic preconditioning. Anesthesiology 2004;100:59-69.

da Silva R, Lucchinetti E., Pasch T, Schaub MC, Zaugg M. Ischemic but not pharmacologic preconditioning elicits a gene expression profile similar to unprotected myocardium. Physiol Genomics 2004;20:117-130.

Clinical applications of preconditioning

Zaugg M, Lucchinetti E, Garcia C, Pasch T, Spahn DR, Schaub MC. REVIEW Part II. Anaesthetics and cardiac preconditioning: clinical implications. Br J Anaesth 2003;91:566-576.

Julier K, da Silva R, Garcia C, Bestmann L, Frascarolo P, Zollinger A, Chassot P-G, Schmid ER, Turina M, von Segesser LK, Pasch T, Spahn DR, Zaugg M. Preconditioning by sevoflurane decreases biochemical markers for myocardial and renal dysfunction in coronary artery bypass graft surgery: a double-blinded placebo-controlled multicenter study. Anesthesiology 2003;98:1315-1327.

Garcia C, Julier K, Bestmann L, Zollinger A, von Segesser LK, Spahn DR, Pasch T, Zaugg M. Preconditioning by sevoflurane decreases PECAM-1 expression and improves one-year cardiovascular outcome in coronary artery bypass graft surgery . Br J Anaesth 2005;94:159-165.