Cytotoxic actions of lidocaine at sublethal concentrations: A model in vitro experiment using rat thymocytes

In order to reveal some cytotoxic features of lidocaine, the effects of lidocaine at sublethal concentrations (10 mM or less) on rat thymocytes were examined by the use of flow-cytometric technique with fluorescent probes. Treatment with lidocaine at 3-10 mM for 1-3 hr significantly increased intracellular Ca and Zn concentrations under normal condition. After the removal of external Ca and Zn, lidocaine still increased intracellular Ca and Zn concentrations, suggesting the lidocaine-induced release of intracellular Ca and Zn. Treatment with lidocaine at 0.3-1 mM for 24 hr significantly increased the populations of dead cells and shrunken cells. Lidocaine at sublethal concentrations exerts some cellular actions that are supposed to be linked to the cytotoxicity. The mechanism of lidocaine-induced cell death varies in timeand concentration-dependent manners.