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 PGE(2) on ROMK-like small-conductance K (SK) channels and Ca(2+)-activated big-conductance K channels (BK) in the cortical collecting duct (CCD). Application of 10 microM PGE(2) 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 PGE(2) on SK channels in the CCD. The effect of PGE(2) 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 PGE(2) stimulates the phosphorylation of P38 and ERK, we treated mouse CCD cells (M-1) with PGE(2). Application of PGE(2) 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 microM PGE(2) increased the phosphorylation of P38 and ERK by 20-21, 50-80, and 80-100%, respectively. The stimulatory effect of PGE(2) on MAPK phosphorylation was not affected by indomethacin but abolished by inhibition of PKC. This suggests that the effect of PGE(2) on MAPK phosphorylation is PKC dependent. Also, the expression of cyclooxygenase II and PGE(2) 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 PGE(2) inhibits SK and BK channels and that there is an effect of PGE(2) on SK channels in the CCD through activation of EP1 receptor and MAPK pathways. Also, high concentrations of PGE(2) induced by K restriction may be partially responsible for increasing MAPK activity during K restriction.