An epoxygenase metabolite of arachidonic acid mediates angiotensin II-induced rises in cytosolic calcium in rabbit proximal tubule epithelial cells.
Previous studies from this and other laboratories have shown that angiotensin II (AII) induces [Ca2+]i transients in proximal tubular epithelium independent of phospholipase C. AII also stimulates formation of 5,6-epoxyeicosatrienoic acid (5,6-EET) from arachidonic acid by a cytochrome P450 epoxygenase and decreases Na+ transport in the same concentration range. Because 5,6-EET mimics AII with regard to Na+ transport, it effects on calcium mobilization were evaluated. [Ca2+]i was measured by video microscopy with the fluorescent indicator fura-2 employing cultured rabbit proximal tubule. AII-induced [Ca2+]i transients were enhanced by arachidonic acid and attenuated by ketoconazole, an inhibitor of cytochrome P450 epoxygenases. Arachidonic acid also elicited a [Ca2+]i transient that was attenuated by ketoconazole. 5,6-EET augmented [Ca2+]i similar to that seen with AII, but was unaffected by ketoconazole. By contrast, the other regioisomers (8,9-, 11,12-, and 14,15-EET) were much less potent. [Ca2+]i transients resulted from influx through verapamil- and nifedipine-sensitive channels. These results suggest a novel mechanism for AII-induced Ca mobilization in proximal tubule involving cytochrome P450-dependent arachidonic acid metabolism and Ca influx through voltage-sensitive channels.
Madhun
Z T
ZT
Department of Medicine, University Hospitals of Cleveland, Ohio.
Goldthwait
D A
DA
McKay
D
D
Hopfer
U
U
Douglas
J G
JG
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D000090762:Cytochrome P-450 CYP2J2; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D007654:Ketoconazole / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D010105:Oxygenases / Q000378:metabolism*; D011817:Rabbits; D015398:Signal Transduction
D001095:Arachidonic Acids; D015220:Calcium Channels; D000804:Angiotensin II; D016718:Arachidonic Acid; C040776:5,6-epoxy-8,11,14-eicosatrienoic acid; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; D000090762:Cytochrome P-450 CYP2J2; D015126:8,11,14-Eicosatrienoic Acid; D007654:Ketoconazole; D002118:Calcium