Elevation of intracellular Ca²⁺ level by triclosan in rat thymic lymphocytes: Increase in membrane Ca²⁺ permeability and induction of intracellular Ca²⁺ release

Triclosan is an antibacterial agent used in household items and personal care products. Because wild animals and humans can harbor this compound in their systems, the toxic effects of triclosan are a possibility and are suspected. Therefore, we examined the effects of triclosan on intracellular Ca²⁺ concentration in rat thymocytes by cytometric techniques using fluorescent probes. Triclosan doses of 1-10μM significantly increased the intensity of Ca²⁺-detecting Fluo-3 fluorescence, indicating an increase in intracellular Ca²⁺ concentrations. The augmentation of Fluo-3 fluorescence became more profound in a dosedependent manner after the addition of an external source of Ca²⁺. Conversely, the removal of external Ca²⁺ greatly attenuated the triclosan-induced augmentation of Fluo-3 fluorescence. These results suggest that triclosan treatment allows external Ca²⁺ to pass through cell membranes. This phenomenon was not specific for Ca²⁺ because externalMn²⁺ quenched the triclosan-induced augmentation of Fluo-3 fluorescence, indicating that triclosan can also mediate Mn²⁺ permeation across membranes. Therefore, these results suggest that triclosan increases membrane permeability to divalent metal cations. Furthermore, triclosan induces Ca²⁺ release from intracellular stores because the Fluo-3 fluorescence inten-sity still increased slightly after triclosan treatment, even under conditions free from external Ca²⁺. Additionally, triclosan did not increase the intensity of Fluo-3 fluorescence when Ca²⁺ was depleted from intracellular Ca²⁺ stores by A23187 under the external Ca²⁺-free condition. Taken together, these data suggest that micromolar concentrations of triclosan affect intracellular Ca²⁺ homeostasis in thymocytes, possibly resulting in cellular malfunction.