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 μM. None of the other EET regioisomers (8,9-, 11,12-, or 14,15-EET; all at 1 μM) affected V(T). This action was also stereoselective, with 5(S),6(R)-EET producing a 2.5-fold greater effect on V(T) than 5(R),6(S)-EET (1 μM each). Like basolateral prostaglandin E₂ (PGE₂), both luminal and basolateral 5,6-EET increased cytosolic Ca²⁺ concentration ([Ca²⁺](i)) in the rabbit CCD. Pretreatment with cyclooxygenase inhibitors (10 μM ibuprofen or 5 μM indomethacin) completely blocked both the [Ca²⁺](i) increase and the change in V(T). Neither 5,6-epoxy-PGE₁ nor 5- hydroxy-PGI₁, cyclooxygenase metabolites of 5,6-EET, affected VT. However, when added to primary cultures of rabbit CCDs, 5,6-EET stimulated endogenous PGE₂ synthesis. We propose that 5,6-EET stimulates endogenous prostaglandin synthesis, which inhibits electrogenic ion transport in the CCD.