Propofol, an anesthetic possessing neuroprotective action against oxidative stress, promotes the process of cell death induced by H2O2 in rat thymocytes.

Propofol (2,6-diisopropylphenol) is a general anesthetic possessing a neuroprotective action against oxidative stress produced by H2O2. H2O2 induces an exposure of phosphatidylserine on outer surface of cell membranes, resulting in change in membrane phospholipid arrangement, in rat thymocytes. Since propofol is highly lipophilic, the agent is presumed to interact with membrane lipids and hence to modify the cell vulnerability to H2O2. Therefore, to test the possibility, we have examined the effect of propofol on rat thymocytes simultaneously incubated with H2O2. Although propofol (up to 30 microM) alone did not significantly affect the cell viability, the agent at 10 microM started to increase the population of dead cells in the presence of 3 mM H2O2 and the significant increase was observed at 30 microM. Propofol at clinically relevant concentrations (10-30 microM) facilitated the process of cell death induced by H2O2 in rat thymocytes. However, propofol protected rat brain neurons against the oxidative stress induced by H2O2 under same experimental condition. Therefore, the action of propofol may be dependent on the type of cells.

Tri-n-butyltin-induced blockade of store-operated calcium influx in rat thymocytes.

Tri-n-butyltin (TBT), one of environmental pollutants, disturbs intracellular Ca(2+) homeostasis by increasing intracellular Ca(2+) concentration ([Ca(2+)]i). Effect of TBT on oscillatory change in [Ca(2+)]i (Ca(2+) oscillation) of rat thymocytes was examined using a laser microscope with fluo-3-AM in order to further elucidate the TBT toxicity related to intracellular Ca(2+). The Ca(2+) oscillation was completely attenuated by 300nM TBT. Since store-operated Ca(2+) channels are involved in the generation of Ca(2+) oscillation, the action of TBT on an increase in [Ca(2+)]i by Ca(2+) influx through store-operated Ca(2+) channels was examined. The increase in [Ca(2+)]i by the store-operated Ca(2+) influx was not affected by 3nM TBT. However, TBT at 10nM or more significantly reduced the increase in [Ca(2+)]i. It is likely that TBT attenuates the Ca(2+) oscillation by reducing the Ca(2+) influx through store-operated Ca(2+) channels.

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 Ca(2+) concentration ([Ca(2+)](i)). DCBS at 1µg/mL (2.87µM) 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 H(2)O(2), an oxidative stress increasing the [Ca(2+)](i). On the other hand, the decrease in extracellular Ca(2+) concentration ([Ca(2+)](e)) increased the cell vulnerability to DCBS and vice versa. Intact membrane lipid bilayer and extracellular Ca(2+) are required to maintain membrane integrity. Therefore, the change of membrane property by manipulation of [Ca(2+)](i) and [Ca(2+)](e) is one of causes for the augmentation of DCBS cytotoxicity.