Effect of triclocarban on membrane potential of rat thymocytes : Assessment with bis-(1,3-dibutylbarbituric acid)trimethine oxonol

The effect of triclocarban (TCC), an　environmental pollutant from household items and health care products, on membrane potential of rat thymocytes was examined by a flow cytometry with a fluorescent probe sensitive to membrane potential, bis-(1,3-dibutylbarbituric acid)trimethine oxonol, because TCC changes intracellular ionic circumstance that may affect the membrane potential. TCC at 0.3 μM or more (up to 3 μM) depolarized the membranes. This TCC-induced phenomenon was against our prediction because TCC increases intracellular Ca2+ concentration that activates Ca2+-dependent K+ channels, resulting in a hyperpolarization. The depolarization was still observed under Ca2+-free condition, but not under Na+-free condition. Furthermore, TCC hyperpolarized the membranes under Ca2+- and Na+-free condition. To see if TCC inhibits Ca2+-dependent hyperpolarization, the effect of A23187, a calcium ionophore, on the membrane potential was examined in the cells treated with TCC. A23187 induced large depolarization in the cells treated with 0.3–3 μM TCC. The A23187-induced depolarization in the presence of TCC was greatly attenuated under Na+-free or Ca2+-free condition whereas A23187 elicited hyperpolarization in the cells treated with 0.3–3 μM TCC under Ca2+- and Na+-free condition. Results suggest that 0.3–3 μM TCC increases membrane permeability of Na+ and Ca2+, resulting in the depolarization. Large depolarization induced by TCC in the presence of external Ca2+ and Na+ may mask the hyperpolarization elicited via the increase in intracellular Ca2+ concentration by TCC. Thus, there is a possibility that TCC depolarizes membranes of lymphocytes, resulting in alteration of cellular functions of lymphocytes.