This study was undertaken to determine if Salviae Radix (SR) exerts protective effect against oxidant-induced inhibition of phosphate uptake in renal proximal tubular cells. Membrane transport function and cell death were evaluated by measuring phosphate uptake and trypan blue exclusion, respectively, in opossum kidney (OK) cells, an established proximal tubular cell line. H₂O₂ was used as a model oxidant. Hz02 inhibited the phosphate uptake in a dose-dependent manner over the concentration range of 0.1-0.5 mM. Similar fashion was observed in cell death. However, the phosphate uptake was more vulnerable to H₂O₂ than cell death, suggesting that H₂O₂-induced inhibition of phosphate uptake is not totally attributed to cell death. Decreasedphosphate uptake was associatsd with ATP depletion and inhibition of Na^+-pump activity as determined by direct inhibition of N^+-K^+-ATPase activity.
When cells were treated with H₂O₂ in the presence of 0.05% SR, the inhibition of phosphate uptake and cell death induced by H_2O-2 was significantly attenuated. SR restored ATP depletion and decreased Na^+-K^+-ATPase activity, and this is likely responsible for the protective effect of SR on decreased phosphate uptake. The protective effect of SR was similar to the H₂O₂ scavenger catalase. SR reacts directly with H₂O₂ to reduce the effective concentration of the oxidant. The iron chelator deferoxamine prevented the inhibition of phosphate uptake and cell death induced by H₂O₂, suggesting that H₂O₂-induced cell injury is resulted from an iron-dependent mechanism.
These results indicate that SR exerts the protective effect against H₂O₂-induced inhibition of phosphate uptake by reacting directly with H₂O₂ like the H₂O₂scavenger enzyme catalase, in OK cells. However, the underlying mechanism remains to be explored.
|