PGE₂ inhibits apical K channels in the CCD through activation of the MAPK pathway

We used the patch-clamp technique and Western blot analysis to explore the effect of PGE₂ on ROMK-like small-conductance K (SK) channels and Ca²⁺-activated big-conductance K channels (BK) in the cortical collecting duct (CCD). Application of 10 μM PGE₂ inhibited SK and BK channels in the CCD. Moreover, either inhibition of PKC or blocking mitogen-activated protein kinase (MAPK), P38 and ERK, abolished the effect of PGE₂ on SK channels in the CCD. The effect of PGE₂ on SK channels was completely blocked in the presence of SC-51089, a specific EP1 receptor antagonist, and mimicked by application of sulprostone, an agonist for EP1 and EP3 receptors. To determine whether PGE₂ stimulates the phosphorylation of P38 and ERK, we treated mouse CCD cells (M-1) with PGE ₂. Application of PGE₂ significantly stimulated the phosphorylation of P38 and ERK within 5 min. The dose-response curve of PGE ₂ effect shows that 1, 5, and 10 μM PGE₂ increased the phosphorylation of P38 and ERK by 20-21, 50-80, and 80-100%, respectively. The stimulatory effect of PGE₂ on MAPK phosphorylation was not affected by indomethacin but abolished by inhibition of PKC. This suggests that the effect of PGE₂ on MAPK phosphorylation is PKC dependent. Also, the expression of cyclooxygenase II and PGE₂ concentration in renal cortex and outer medulla was significantly higher in rats fed a K-deficient diet than those on a normal-K diet. We conclude that PGE₂ inhibits SK and BK channels and that there is an effect of PGE₂ on SK channels in the CCD through activation of EP1 receptor and MAPK pathways. Also, high concentrations of PGE₂ induced by K restriction may be partially responsible for increasing MAPK activity during K restriction.