Modification of vulnerability to dodecylbenzenesulfonate, an anionic surfactant, by calcium in rat thymocytes

We have previously reported that cremophor EL, a nonionic surfactant, at clinical concentrations significantly decreases the cell viability of rat thymocytes with phosphatidylserine-exposed (PS-exposed) membranes under in vitro condition. It is reminiscent of a possibility that sodium dodecylbenzenesulfonate (DCBS), an anionic surfactant world-widely used for detergents, also affects the cells in the similar manner. To test the possibility, the effect of DCBS on rat thymocytes has been examined using a flow cytometer with fluorescent probes. Exposure of PS on outer surface of cell membranes was induced by A23187, a calcium ionophore to increase intracellular Ca2+ concentration ([Ca2+]i). DCBS at 1 μg/mL (2.87 μM) significantly decreased the viability of cells with PS-exposed membranes, but not with intact membranes. DCBS also significantly decreased the viability of cells exposed to H2O2, an oxidative stress increasing the [Ca2+]i. On the other hand, the decrease in extracellular Ca2+ concentration ([Ca2+]e) increased the cell vulnerability to DCBS and vice versa. Intact membrane lipid bilayer and extracellular Ca2+ are required to maintain membrane integrity. Therefore, the change of membrane property by manipulation of [Ca2+]i and [Ca2+]e is one of causes for the augmentation of DCBS cytotoxicity.