Isoflurane Activates Human Cardiac Mitochondrial Adenosine Triphosphate-Sensitive K+ Channels Reconstituted in Lipid Bilayers

In Brief BACKGROUND: Activation of the mitochondrial adenosine triphosphate (ATP)-sensitive K+ channel (mitoKATP) has been proposed as a critical step in myocardial protection by isoflurane-induced preconditioning in humans and animals. Recent evidence suggests that reactive oxygen species (ROS) may mediate isoflurane-mediated myocardial protection. In this study, we examined the direct effect of isoflurane and ROS on human cardiac mitoKATP channels reconstituted into the lipid bilayers. METHODS: Inner mitochondrial membranes were isolated from explanted human left ventricles not suitable for heart transplantation and fused into lipid bilayers in symmetrical potassium glutamate solution (150 mM). ATP-sensitive K+ currents were recorded before and after exposure to isoflurane and H2O2 under voltage clamp. RESULTS: The human mitoKATP was identified by its sensitivity to inhibition by ATP and 5-hydroxydecanoate. Addition of isoflurane (0.8 mM) increased the open probability of the mitoKATP channels, either in the presence or absence of ATP inhibition (0.5 mM). The isoflurane-mediated increase in K+ currents was completely inhibited by 5-hydroxydecanoate. Similarly, H2O2 (200 μM) was able to activate the mitoKATP previously inhibited by ATP. CONCLUSIONS: These data confirm that isoflurane, as well as ROS, directly activates reconstituted human cardiac mitoKATP channel in vitro, without apparent involvement of cytosolic protein kinases, as commonly proposed. Activation of the mitoKATP channel may contribute to the myocardial protective effect of isoflurane in the human heart. IMPLICATIONS: Brief exposure to volatile anesthetics protects the heart against subsequent myocardial ischemia, a phenomenon known as “anesthetic-induced cardiac preconditioning.” Here we present evidence showing that the human cardiac mitochondrial KATP channel, reconstituted in lipid bilayers, can be directly activated by isoflurane. This activation apparently does not require the translocation of cytosolic kinases, as previously proposed, in anesthetic-induced preconditioning.