BACKGROUND: It is known that bupivacaine induce cell death in several immortalized cells. However, there is no report concerning bupivacaine-induced cell death in the primary cultured cardiomyocytes. We compared the direct cytotoxicity of local anesthetics in cardiomyocytes. Furthermore, the mechanisms of cell death were evaluated.

METHODS: The myocardial cells of rat pups were cultured 3 days after seeding. The methyltetrazolium (MTT) assay was employed to quantify differences in cellular viability. To confirm apoptosis, Hoechst-propidium iodide staining, DNA fragmentation by electrophoresis and western blot analysis were performed. And to examine the mechanisms of cell death, intracellular calcium and expression levels of mitogen-activated protein kinases (MAPKs) family members were evaluated.

RESULTS: Among the local anesthetics under 1 mM concentration for 18 h, only bupivacaine significantly decreased the MTT activity (P < 0.001). Bupivacaine induced cell death in a dose-responsive and time dependent manner. Cell death showed apoptotic characteristics, such as DNA fragmentation, chromatin condensation, decrease of precursor caspase-3 protein level, increased cleaved PARP, and cytochrome C release into the cytoplasm. Bupivacaine phosphorylated three major MAPKs, i.e. extracellular signal-regulated kinases (ERKs), p38 kinase and c-Jun N-terminal kinases (JNKs) stress-activated protein kinases. Administration of ERK inhibitor increase cell death, whereas inhibitors of p38 kinase and JNK decreased cell death (P < 0.05). In addition, the intracellular calcium level was approximately 4 times higher after the bupivacaine treatment (P < 0.001), which was inhibited by calcium chelators (P < 0.001). Calcium chelators inhibited expression of MAPKs.

CONCLUSIONS: In bupivacaine-induced apoptosis in cardiomyocytes, intracellular calcium increase and MAPKs family plays important roles.