Comparison of the effects of bupivacaine and ropivacaine on heart cell mitochondrial bioenergetics

Background: High lipophilic local anesthetics interfere with mitochondrial energy metabolism. These metabolic effects could in part explain some of the toxic effects of local anesthetics, such as bupivacaine-induced myocardial depression. The aim of this study was to compare the bioenergetic effects of the local anesthetics bupivacaine and ropivacaine. Methods: The effects of both local anesthetics on mitochondrial energy metabolism mere studied in rat heart isolated mitochondria and in saponin-skinned left ventricle fibers. Oxygen consumption, adenosine triphosphate synthesis, and enzymatic activities of the complexes of the respiratory chain were measured. Results: Bupivacaine and ropivacaine acted, in isolated mitochondria, as uncouplers between oxygen consumption and phosphorylation of adenosine diphosphate. Further, an inhibitory effect of mitochondrial respiration was evidenced with both anesthetics during maximal respiration and was assigned to a direct inhibition of complex I of the respiratory chain. Mitochondrial adenosine triphosphate synthesis was decreased by both mechanisms. However, both in isolated mitochondria and in permeabilized heart fibers, ropivacaine was less potent than bupivacaine. Adenosine triphosphate synthesis was completely suppressed at 3 nM (similar to 0.1%) bupivacaine, whereas 3 mM ropivacaine induced only about a 40% inhibition. Conclusions: Ropivacaine disturbs mitochondrial energy metabolism less than bupivacaine does. The lower lipid solubility of ropivacaine may be responsible for the lesser dose-dependent effects of this drug on mitochondrial bioenergetics.