5,6-EET INHIBITS ION-TRANSPORT IN COLLECTING DUCT BY STIMULATING ENDOGENOUS PROSTAGLANDIN SYNTHESIS

We examined the mechanism by which the cytochrome P-450 metabolite of arachidonate, 5,6-epoxyeicosatrienoic acid (5,6-EET), modulates electrogenic transport in the rabbit cortical collecting duct (CCD). 5,6-EET depolarized transepithelial voltage (V-T) in a concentration-dependent manner with a maximal effect at 1 mu M. None of the other EET regioisomers (8,9-, 11,12-, or 14,15-EET; all at 1 mu M) affected V-T. This action was also stereoselective, with 5(S),G(R)-EET producing a 2.5-fold greater effect on V-T than 5(R),6(S)-EET (1 mu M each). Like basolateral prostaglandin E(2) (PGE(2)), both luminal and basolateral 5,6-EET increased cytosolic Ca2+ concentration ([Ca2+](i)) in the rabbit CCD. Pretreatment with cyclooxygenase inhibitors (10 mu M ibuprofen or 5 mu M indomethacin) completely blocked both the [Ca2+]i increase and the change in V-T Neither 5,B-epoxy-PGE(1) nor 5-hydroxy-PGI(1), cyclooxygenase metabolites of 5,6-EET, affected V-T. However, when added to primary cultures of rabbit CCDs, 5,6-EET stimulated endogenous PGE(2) synthesis. We propose that 5,6-EET stimulates endogenous prostaglandin synthesis, which inhibits electrogenic ion transport in the CCD.