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-KATP). 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-KATP elicited by pinacidil (20 mum) was 18.9 +/- 1.8 pA/pF (n = 11). In the presence of isoflurane (0.55 mm), the density of pinacidil-activated I-KATP 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-KATP 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 mum N-acetyl-L-cysteine, respectively. Concurrent application of isoflurane and carnosine (100 gm), superoxide dismutase (100 U/ml), or catalase (100 U/ml) attenuated the densities of I-KATP 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-KATP by pinacidil alone. 5-Hydroxy-decanoate (100 mum) did not alter the sensitization effect by isoflurane, and the density of I-KATP in this group was 37.1 +/- 3.8 pA/pF (n = 6). Conclusion. 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.