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 Ca concentration that activates Ca-dependent K channels, resulting in a hyperpolarization. The depolarization was still observed under Ca-free condition, but not under Na-free condition. Furthermore, TCC hyperpolarized the membranes under Caand Na-free condition. To see if TCC inhibits Ca-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 Ca-free condition whereas A23187 elicited hyperpolarization in the cells treated with 0.3–3 μM TCC under Caand Na-free condition. Results suggest that 0.3–3 μM TCC increases membrane permeability of Na and Ca, resulting in the depolarization. Large depolarization induced by TCC in the presence of external Ca and Na may mask the hyperpolarization elicited via the increase in intracellular Ca concentration by TCC. Thus, there is a possibility that TCC depolarizes membranes of lymphocytes, resulting in alteration of cellular functions of lymphocytes.