An epoxygenase metabolite of arachidonic acid mediates angiotensin II-induced rises in cytosolic calcium in rabbit proximal tubule epithelial cells.

Abstract

Previous studies from this and other laboratories have shown that angiotensin II (AII) induces [Ca2"j 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, its effects on calcium mobilization were evaluated. ICa2i, was measured by video microscopy with the fluorescent indicator fura-2 employing cultured rabbit proximal tubule. AII-induced ICa2+i transients were enhanced by arachidonic acid and attenuated by ketoconazole, an inhibitor of cytochrome P450 epoxygenases. Arachidonic acid also elicited a ICa2i1, transient that was attenuated by ketoconazole. 5,6-EET augmented (Ca2'], 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. ICa2+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 asid metabolism and Ca influx through voltage-sensitive channels. (J. Clin. Invest. 1991.

Calcium Influx Factor, Further Evidence It Is 5,6-Epoxyeicosatrienoic Acid

“…Our previous results suggest that the link to CIF requires the activation of cPLA 2 and release of arachidonic acid from cellular phospholipids in U937 cells (8). Other groups have reported similar correlations between arachidonic acid release and calcium influx (43,44). Cytochrome P450 activity has also been coupled to the formation of CIF (45,46) and is one of the major pathways through which arachidonic acid is metabolized.…”

Arachidonic Acid Metabolites Inhibit the Stimulatory Effect of Angiotensin II in Renal Proximal Tubules

“…Similarly, we also failed to detect a significant cell Ca 2+ increase in the presence of 10 − 7 mol/L arachidonic acid ( n = 8). On the other hand, Douglas and colleagues also reported that incubating a cell culture with arachidonic acid significantly enhances the Ang II-induced cell Ca 2+ increase ( 24 ). As shown in Fig.…”

“…Douglas and colleagues, however, reported different mechanisms for cell Ca 2+ increase. On the basis of data obtained from cultured rabbit proximal tubular cells, they proposed that Ang II-induced Ca 2+ increases in proximal tubules arise secondary to the release of arachidonic acid and the production of 5,6-EET ( 24 ). To test whether a similar mechanism operates in intact proximal tubules, we measured cell Ca 2+ concentrations in wild-type mice.…”

Involvement of cAMP-response element binding protein-1 in arachidonic acid-induced vascular smooth muscle cell motility

“…Earlier studies have shown that the CYP epoxygenase products of AA, such as 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids, inhibit platelet-derived growth factor-BB-induced and serum-induced VSMC motility (40). To understand whether AA-induced VSMC motility requires its conversion via the CYP epoxygenases, we next studied the effects of SKF525A and ketoconazole, two potent and specific inhibitors of this enzymatic pathway (40,41). Neither SKF525A (100 mM) nor ketoconazole (20 mM) inhibited AA-induced VSMC motility (Fig.…”