Increased responsiveness to JNK1/2 mediates the enhanced H2O2-induced stimulation of Cl/HCO3 exchanger activity in immortalized renal proximal tubular epithelial cells from the SHR

We have previously demonstrated that exogenous H₂O₂ stimulates Cl⁻/HCO₃⁻ exchanger activity in immortalized renal proximal tubular epithelial (PTE) cells from both the Wistar-Kyoto (WKY) rat and the spontaneously hypertensive rat (SHR), this effect being more pronounced in SHR cells. The aim of the present study was to examine the mechanism of H₂O₂-induced stimulation of Cl⁻/HCO₃⁻ exchanger activity in WKY and SHR cells. It is now reported that the SHR PTE cells were endowed with an enhanced capacity to produce H₂O₂, comparatively with WKY cells and this was accompanied by a decreased expression of SOD2, SOD3, and catalase in SHR PTE cells. The stimulatory effect of H₂O₂ on the exchanger activity was blocked by SP600125 (JNK inhibitor), but not by U0126 (MEK1/2 inhibitor) or SB203580 (p38 inhibitor) in both cell lines. Basal JNK1 and JNK2 protein expression was higher in SHR PTE cells than in WKY PTE cells. H₂O₂ had no effect on p-JNK1/2 in WKY PTE cells over time. By contrast, H₂O₂ treatment resulted in a rapid and sustained increase in JNK1/2 phosphorylation in SHR PTE cells, which was completely abolished by apocynin. Treatment of SHR PTE cells with apocynin significantly decreased the H₂O₂-induced stimulation of Cl⁻/HCO₃⁻ exchanger activity. It is concluded that H₂O₂-induced stimulation of Cl⁻/HCO₃⁻ exchanger activity is regulated by JNK1/2, particularly by JNK2, in SHR PTE cells. The imbalance between oxidant and antioxidant mechanisms in SHR PTE cells enhances the response of JNK1/2 to H₂O₂, which contributes to their increased sensitivity to H₂O₂.