Myocardial Protection by Isoflurane Preconditioning Preserves Ca2+ Cycling Proteins Independent of Sarcolemmal and Mitochondrial KATP Channels

In Brief INTRODUCTION: Anesthetic preconditioning (APC) with volatile anesthetics improves recovery of contractile function and reduces calcium overload after ischemia/reperfusion (I/R). Mitochondrial and sarcolemmal KATP channel openings have been implicated in APC-induced cardioprotection. In this study, we investigated the effect of APC on major calcium cycling proteins and its relation to KATP channels. METHODS: Isolated perfused rat hearts were divided into seven groups: Time control (n = 10), ischemia control (n = 8), APC (n = 8), Mitochondrial KATP inhibitor 5-hydroxydecanoate (5-HD, 200 μM, n = 8), Sarcolemmal KATP inhibitor HMR1098 (HMR, 20 μM, n = 8), and APC plus 5-HD or APC plus HMR1098 (n = 8 each). APC was initiated by administering 1.5% isoflurane for 15 min, followed by a 15 min washout before 30 min of myocardial ischemia and 60 min of reperfusion. Ca2+-release channels (RyR2), Ca2+-adenosine triphosphatase (SERCA2a), phospholamban, plasma membrane Ca2+ ATPase, and sodium–calcium exchanger in the homogenate were determined by Western blot assay. RESULTS: APC improved contractile recovery (left ventricular developed pressure, +dP/dt, −dP/dt) after I/R, which was blocked by 5-HD and HMR. I/R depressed the density of RyR2, SERCA2a, and phospholamban, with no changes in the density of plasma membrane Ca2+ ATPase and sodium–calcium exchanger. APC reversed I/R-induced degradation of RyR2 and SERCA2a in the presence or absence of 5HD and HMR. CONCLUSIONS: I/R-induced depression in cardiac performance is associated with a down-regulation of the major sarcoplasmic reticulum Ca2+-cycling proteins. Anesthesia preconditioning with isoflurane prevents I/R-related degradation of the RyR2 and SERCA2a in the sarcoplasmic reticulum. However, this effect was independent of its activation of KATP channels. IMPLICATIONS: In isolated perfused rat hearts, isoflurane preconditioning was found to preserve Ca2+ cycling proteins in sarcoplasmic reticulum during ischemia/reperfusion. This protection, however, does not depend on its activation of the KATP channels. Our results imply that isoflurane preconditioning may activate mechanisms that inhibit protease activity during ischemia/reperfusion.