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.
Jiang
Ming T
MT
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA. mtjiang@mcw.edu
Nakae
Yuri
Y
Ljubkovic
Marko
M
Kwok
Wai-Meng
WM
Stowe
David F
DF
Bosnjak
Zeljko J
ZJ
D000255:Adenosine Triphosphate / Q000378:metabolism*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D066298:In Vitro Techniques; D019157:Ischemic Preconditioning, Myocardial; D007530:Isoflurane / Q000494:pharmacology*; D008051:Lipid Bilayers / Q000378:metabolism; D008929:Mitochondria, Heart / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000494:pharmacology
D018685:Anesthetics, Inhalation; D008051:Lipid Bilayers; D015221:Potassium Channels; D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D007530:Isoflurane