Contribution of reactive oxygen species to isoflurane-induced sensitization of cardiac sarcolemmal adenosine triphosphate-sensitive potassium channel to pinacidil.
BACKGROUND
Myocardial protection by volatile anesthetics involves activation of cardiac adenosine triphosphate-sensitive potassium (K(ATP)) channels. The authors have previously shown that isoflurane enhances sensitivity of the sarcolemmal K(ATP) channel to the opener, pinacidil. Because reactive oxygen species seem to be mediators in anesthetic preconditioning, the authors investigated whether they contribute to the mechanism of the sensitization effect by isoflurane.


METHODS
Ventricular myocytes were isolated from guinea pig hearts for the whole cell patch clamp recordings of the sarcolemmal K(ATP) channel current (I(KAPT)). Free radical scavengers N-acetyl-L-cysteine, carnosine, superoxide dismutase, and catalase were used to investigate whether reactive oxygen species mediate isoflurane facilitation of the channel opening by pinacidil. A possible role of the mitochondrial K(ATP) channels was tested using a blocker of these channels, 5-hydroxydecanoate.


RESULTS
The mean density (+/- SEM) of I(KAPT) elicited by pinacidil (20 microM) was 18.9 +/- 1.8 pA/pF (n = 11). In the presence of isoflurane (0.55 mM), the density of pinacidil-activated I(KAPT) increased to 38.5 +/- 2.4 pA/pF (n = 9). Concurrent application of isoflurane and N-acetyl-L-cysteine decreased the sensitization effect by isoflurane in a concentration-dependent manner, whereby the densities of I(KAPT) were 32.6 +/- 1.4 (n = 6), 26.2 +/- 2.3 (n = 6), and 19.4 +/- 2.1 pA/pF (n = 8) at 100, 250, and 500 microM N-acetyl-L-cysteine, respectively. Concurrent application of isoflurane and carnosine (100 microM), superoxide dismutase (100 U/ml), or catalase (100 U/ml) attenuated the densities of I(KAPT) to 27.9 +/- 2.6, 27.2 +/- 2.9, and 25.9 +/- 2.2 pA/pF, respectively. None of the scavengers affected activation of I(KAPT) by pinacidil alone. 5-Hydroxydecanoate (100 microM) did not alter the sensitization effect by isoflurane, and the density of I(KAPT) in this group was 37.1 +/- 3.8 pA/pF (n= 6).


CONCLUSIONS
These results suggest that reactive oxygen species contribute to the mechanism by which isoflurane sensitizes the cardiac sarcolemmal K(ATP) channel to the opener, pinacidil.
An
Jianzhong
J
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
Stadnicka
Anna
A
Kwok
Wai-Meng
WM
Bosnjak
Zeljko J
ZJ
D000111:Acetylcysteine / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002336:Carnosine / Q000494:pharmacology; D002374:Catalase / Q000378:metabolism; D002469:Cell Separation; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007530:Isoflurane / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000819:agonists / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects; D018408:Patch-Clamp Techniques; D020110:Pinacidil / Q000494:pharmacology*; D015221:Potassium Channels; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D014665:Vasodilator Agents / Q000494:pharmacology*
D018685:Anesthetics, Inhalation; D008565:Membrane Proteins; D015221:Potassium Channels; D017382:Reactive Oxygen Species; D014665:Vasodilator Agents; C117780:mitochondrial K(ATP) channel; D020110:Pinacidil; D002336:Carnosine; D007530:Isoflurane; D002374:Catalase; D013482:Superoxide Dismutase; D000111:Acetylcysteine