Expression of the OAT gene in MC3T3-E1. (A) OAT gene expression was determined by real time-polymerase chain reaction using RNA extracts. The expression of OAT-3 was relatively higher than that of OAT-1. The data represent the mean ± SEM (n = 3 for each group). (B) Probenecid (20 mM), an OAT inhibitor, reduced IS-induced cell toxicity, which is similar to an antioxidant effect. OAT is an IS transporter in MC3T3-E1 cells. The data represent the mean ± SEM from six determinations in each group. (C) IS-induced free radical production was suppressed by probenecid and antioxidants. The data represent the mean from six replicates in each group. OAT, organic anion transport; IS: indoxyl sulfate. *P < 0.05 vs control, ** P < 0.05 vs IS.