Tetracaine decreases intracellular Zn2+ concentration by inhibiting Zn2+ influx in rat thymocytes

In this study to examine the cytotoxic property of tetracaine, we cytometrically examined the effect of tetracaine on intracellular Zn2+ concentration by the use of FluoZin-3, a fluorescent indicator of intracellular Zn2+. Lidocaine was used as a reference drug. The incubation of rat thymocytes with tetracaine decreased the intensity of FluoZin-3 fluorescence while that with lidocaine increased the intensity. The incubation with 10 μM DTPA, a chelator for extracellular Zn2+, attenuated the tetracaine-induced decrease in fluorescence intensity. The application of ZnCl2 augmented FluoZin-3 fluorescence. The augmentation by ZnCl2 was a temperature-sensitive. Tetracaine attenuated the ZnCl2-induced augmentation of FluoZin-3 fluorescence. Taken together, the results suggest that tetracaine attenuates membrane Zn2+ influx, resulting in a decrease in intracellular Zn2+ concentration in rat thymocytes. Although the cells in this study are not targets for actions of local anesthetics, the result may give one clue to explain the difference between the cytotoxicity of local anesthetics since the action of tetracaine on FluoZin-3 fluorescence was opposite to that of lidocaine.