shows the effect of Mrp inhibitors and PAPM on [3H]VPA uptake by IOVs. In the presence of ATP, [3H]VPA uptake was inhibited by Mrp inhibitors (indomethacin, TCA, and PGE1), as well as by PAPM. In contrast, the uptake of [3H]VPA in the presence of AMP was significantly lower than that in the presence of ATP, and was not inhibited by these compounds.