Isoflurane activates human cardiac mitochondrial adenosine triphosphate-sensitive K+ channels reconstituted in lipid bilayers.

BACKGROUND: Activation of the mitochondrial adenosine triphosphate (ATP)-sensitive K+ channel (mitoK(ATP)) 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 mitoK(ATP) 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 mitoK(ATP) was identified by its sensitivity to inhibition by ATP and 5-hydroxydecanoate. Addition of isoflurane (0.8 mM) increased the open probability of the mitoK(ATP) 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 microM) was able to activate the mitoK(ATP) previously inhibited by ATP. CONCLUSIONS: These data confirm that isoflurane, as well as ROS, directly activates reconstituted human cardiac mitoK(ATP) channel in vitro, without apparent involvement of cytosolic protein kinases, as commonly proposed. Activation of the mitoK(ATP) channel may contribute to the myocardial protective effect of isoflurane in the human heart.

Increasing heart size and age attenuate anesthetic preconditioning in guinea pig isolated hearts.

Anesthetic preconditioning (APC) reduces myocardial ischemia/reperfusion injury. Recent investigations have reported that older hearts are not susceptible to APC. We investigated if increasing heart size with age determines the susceptibility to APC in young guinea pigs. Langendorff-prepared guinea pig hearts of different weights (1.1-2.2 g) and ages (2-7 wks) were exposed to 1.3 mM sevoflurane for 15 min followed by 30 min washout (APC; n = 20) before 30 min global ischemia and 120 min reperfusion. Control hearts (n = 20) were not subject to APC. Left ventricular pressure was measured isovolumetrically and infarct size was determined by triphenyltetrazolium staining. Functional data were not different between groups at the beginning of the experiments nor did they correlate with heart weight or age. At 120 min reperfusion, left ventricular pressure, coronary flow, and tissue viability showed significant negative correlations with increasing heart weight and age in APC but not in control hearts; i.e., APC improved function and attenuated infarct size better in smaller/younger hearts than in larger/older hearts. Thus, increasing age and heart size attenuate the susceptibility for APC even in younger guinea pigs. This may have important implications for further basic science research and the possible clinical applicability of APC in humans.

Anesthetic preconditioning: the role of free radicals in sevoflurane-induced attenuation of mitochondrial electron transport in Guinea pig isolated hearts.

Cardioprotection by anesthetic preconditioning (APC) can be abolished by nitric oxide (NO*) synthase inhibitors or by reactive oxygen species (ROS) scavengers. We previously reported attenuated mitochondrial electron transport (ET) and increased ROS generation during preconditioning sevoflurane exposure as part of the triggering mechanism of APC. We hypothesized that NO* and other ROS mediate anesthetic-induced ET attenuation. Cardiac function and reduced nicotinamide adenine dinucleotide (NADH) fluorescence, an index of mitochondrial ET, were measured online in 68 Langendorff-prepared guinea pig hearts. Hearts underwent 30 min of global ischemia and 120 min of reperfusion. Before ischemia, hearts were temporarily perfused with superoxide dismutase, catalase, and glutathione to scavenge ROS or N(G)-nitro-L-arginine-methyl-ester (L-NAME) to inhibit NO* synthase in the presence or absence of 1.3 mM sevoflurane (APC). APC temporarily increased NADH before ischemia, i.e., it attenuated mitochondrial ET. Both this NADH increase and the cardioprotection by APC on reperfusion were prevented by superoxide dismutase, catalase, and glutathione and by N(G)-nitro-L-arginine-methyl-ester. Thus, ROS and NO*, or reaction products including peroxynitrite, mediate sevoflurane-induced ET attenuation. This may lead to a positive feedback mechanism with augmented ROS generation to trigger APC secondary to altered mitochondrial function.