Preconditioning by isoflurane induces lasting sensitization of the cardiac sarcolemmal adenosine triphosphate-sensitive potassium channel by a protein kinase c-delta-mediated mechanism

Background: Cardioprotective effects of volatile anesthetics in anesthetic-induced preconditioning involve activation of the cardiac sarcolemmal adenosine triphosphate-sensitive potassium (sarcK(ATP)) channels. This study addressed the memory phase of anesthetic preconditioning by investigating whether brief exposure to isoflurane produces lasting sensitization of the sarcK(ATP), channel and whether protein kinase C mediates this effect. Methods: Whole cell sarcK(ATP) channel current (I-KATP) was monitored from single isolated rat ventricular cardiomyocytes. Pinacidil was used to open the channel, and the magnitude of activated I-KATP was an indicator of channel's ability to open. Involvement of protein kinase C was investigated using chelerythrine and isoform-specific peptide inhibitors and activators of protein kinase C-delta and protein kinase C-epsilon. Results: The mean density of I-KATP, elicited by pinacidil (5 pm) in anesthetic-free conditions was 3.8 +/- 3.7 pA/pF (n = 11). After 10 min of exposure to isoflurane (0.56 mm) and 10 or 30 min of anesthetic washout, pinacidil-elicited I-KATP was increased to 15.6 +/- 11.3 pA/pF (n = 12; P < 0.05) and 11.8 +/- 3.9 pA/pF (n = 6; P < 0.05), respectively. In the presence of chelerythrine (5 mu m), isoflurane did not potentiate channel opening, and I-KATP was 6.6 +/- 4.6 pA/pF (n = 11). Application of protein kinase C-delta peptide inhibitor also abolished isoflurane-induced sensitization of sarcK(ATP) channel, and I-KATP was 7.7 +/- 5.4 pA/pF (n = 12). In contrast, protein kinase C-E peptide inhibitor did not affect channel sensitization, and pinacidil-elicited current was 14.8 +/- 9.6 pA/pF (n = 12). Interestingly, when both protein kinase C-delta and protein kinase C-epsilon activators were applied instead of isoflurane, they sensitized the channel to the same extent as isoflurane (18.9 +/- 7.2 pA/pF, n = 11, and 18.6 +/- 11.1 pA/pF, n = 10, respectively). Conclusion: Isoflurane induces prolonged sensitization of the sarcK(ATP) channel to opening that persists even after anesthetic withdrawal. Our results indicate that protein kinase C-delta, rather than protein kinase C-epsilon, is a likely mediator of isoflurane effects, although both protein kinase C-delta and protein kinase C-epsilon can modulate the channel function.