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 1-10 mu M 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 dose-dependent 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 external Mn2+ 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 intensity still increased slightly after triclosan treatment, even under conditions free from external Calf. 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.