An epoxygenase metabolite of arachidonic acid 5,6 epoxy-eicosatrienoic acid mediates angiotensin-induced natriuresis in proximal tubular epithelium.
Several laboratories have documented that angiotensin II (AII) induces natriuresis in proximal tubular epithelium by a mechanism that has as yet not been disclosed. The present studies were designed to test the hypothesis that cytochrome P450-dependent metabolites of arachidonic acid mediate this effect. In cultured rabbit proximal tubule a ketoconazole-sensitive product comigrating with 5,6-epoxy-eicosatrienoic acid (5,6-EET) on reverse phase and normal phase HPLC was stimulated two-fold by AII. We employed cultures of early S1 segments on a modified Ussing chamber as a bioassay to evaluate the effects of AII and 5,6-EET on unidirectional 22Na (apical to basolateral) flux (JNa). AII inhibited JNa, an effect that was abolished by ketoconazole. Furthermore, 5,6-EET decreased JNa in a manner analogous to AII, and the effect was potentiated by inhibition of endogenous 5,6-EET production. Employing the Ca2(+)-sensitive fluorescent probe, Fura 2, we observed a dose-dependent increase in [Ca2+]i with nM to microM 5,6-EET, effects that were abolished by depletion of extracellular Ca2+ and voltage-sensitive Ca-channel blockers. These observations support the hypothesis that 5,6-EET represents the second messenger that mediates AII-induced natriuresis via stimulation of Ca2+ influx through voltage-sensitive channels.
Romero
M F
MF
Department of Medicine, University Hospitals of Cleveland, Case Western Reserve University School of Medicine, Ohio 44106.
Madhun
Z T
ZT
Hopfer
U
U
Douglas
J G
JG
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D000090762:Cytochrome P-450 CYP2J2; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D009318:Natriuresis / Q000187:drug effects*; D010105:Oxygenases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D011817:Rabbits; D015290:Second Messenger Systems; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
D001095:Arachidonic Acids; D000804:Angiotensin II; D016718:Arachidonic Acid; C040776:5,6-epoxy-8,11,14-eicosatrienoic acid; D003577:Cytochrome P-450 Enzyme System; D012964:Sodium; D010105:Oxygenases; D000090762:Cytochrome P-450 CYP2J2; D010741:Phospholipases A; D000254:Sodium-Potassium-Exchanging ATPase; D015126:8,11,14-Eicosatrienoic Acid; D002118:Calcium