Ablation of small conductance calcium-activated potassium type-2 channel (SK ₂ ) delays occurrence of bupivacaine-induced cardiotoxicity in isolated mouse hearts

Bupivacaine is frequently used for conducting regional anesthesia. When accidentally injected or excessively absorbed into circulation, bupivacaine can induce severe arrhythmia and potentially lead to cardiac arrest. The specific mechanisms underlying this cardiotoxicity, however, remain to be clarified. We transfected HEK-293 cells to express the small conductance calcium-activated potassium type-2 channel (SK 2 ), and used a whole-cell patch clamp method in order to explore how bupivacaine affected these channels. We subsequently used SK 2 knockout mice to explore the relevance of SK 2 channels in bupivacaine-induced cardiotoxicity in isolating mouse hearts, mounting them on a Langendorff apparatus, and perfusing them with bupivacaine. Using this system, arrhythmia, asystole, and cardiac functions were monitored. We observed dose-dependent inhibition of SK 2 channels by bupivacaine: half-maximal inhibitory concentration (IC50) value = 18.6 μM (95% CI 10.8–32.1). When SK 2 knockout (SK 2 −/− ) or wild-type (WT) mice were perfused with Krebs-Henseleit buffer (KHB), we did not observe any instances of arrhythmia. When SK 2 −/− mice or WT were perfused with KHB containing bupivacaine (40 μM), the time to arrhythmia (T arrhythmia ) and time to asystole (T asystole ) were both significantly longer in SK 2 −/− mice relative to WT mice ( P < 0.001). Similarly, SK 2 −/− mice exhibited a significantly longer time to 25%, 50%, and 75% reductions in heart rate (HR) and rate-pressure product (RPP) relative to WT mice following bupivacaine perfusion ( P < 0.001). These results reveal that bupivacaine was able to mediate a dose-dependent inhibition of SK 2 channels in HEK-293 cells, and deletion of SK 2 channels can delay bupivacaine-induced cardiotoxicity in isolated mouse hearts.