title: Epoxyeicosatrienoic acids activate Na+/H+ exchange and are mitogenic in cultured rat glomerular mesangial cells.
abstract: The present study examined responses of cultured rat glomerular mesangial cells to exogenous exposure of epoxyeicosatrienoic acids (EET's), products of cytochrome P450 epoxygenase. One day after administration of 8,9- or 14,15-EET, cultured rat mesangial cells demonstrated significant increases in [3H]thymidine incorporation (10(-7) M 14,15-EET: 120 +/- 7% of control; n = 6; P less than 0.025; 10(-6) M 14,15-EET: 145 +/- 10%; n = 20; P less than 0.0005; 10(-6) M 8,9-EET: 167 +/- 31%; n = 9; P less than 0.05), which was not affected by addition of the cyclooxygenase inhibitor indomethacin. In addition to stimulation of [3H]thymidine incorporation, the epoxides stimulated mesangial cell proliferation. 14,15-EET administration induced intracellular alkalinization of 0.2-0.3 pH units, which was prevented by extracellular Na+ removal and blunted by amiloride (0.5 mM). Following intracellular acidification with NH4Cl addition and removal, greater than 85% of 3 mM 22Na uptake into mesangial cells was inhibited by 1 mM amiloride, indicating Na+/H+ exchange. Under these conditions, 14,15-EET stimulated Na+/H+ exchange by 42% and 8,9-EET stimulated Na+/H+ exchange by 59%. Neither protein kinase C depletion nor addition of the protein kinase C inhibitor, staurosporine, affected this stimulation. In [3H]myo-inositol loaded mesangial cells, no significant stimulation of phosphoinositide hydrolysis was detected in response to administration of 14,15-EET. Twenty-four hours after addition of [14C]14,15-EET, greater than 90% was preferentially esterified to cellular lipids, with predominant incorporation into phosphatidylinositol, phosphatidylethanolamine, and diacylglycerol. Thus, these results demonstrate epoxyeicosatrienoic acids stimulate Na+/H+ exchange and mitogenesis in mesangial cells. These effects do not appear to be mediated via phospholipase C activation. In addition, 14,15-EET was selectively incorporated into cellular lipids known to mediate signal transduction. These observations extend the potential biologic roles of c-P450 arachidonate metabolites to include stimulation of cell proliferation and suggest a role for these compounds in vascular and renal injury.
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: R C
authors.initials: RC
authors.lastname: Harris
authors.forename: T
authors.initials: T
authors.lastname: Homma
authors.forename: H R
authors.initials: HR
authors.lastname: Jacobson
authors.forename: J
authors.initials: J
authors.lastname: Capdevila
mesh_terms: D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005920:Glomerular Mesangium / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D008934:Mitogens / Q000494:pharmacology; D051381:Rats; D017923:Sodium-Hydrogen Exchangers; D013936:Thymidine / Q000378:metabolism
chemical_list: D001095:Arachidonic Acids; D002352:Carrier Proteins; D005231:Fatty Acids, Unsaturated; D008934:Mitogens; D017923:Sodium-Hydrogen Exchangers; C050715:8,9-epoxyeicosatrienoic acid; C046782:14,15-epoxy-5,8,11-eicosatrienoic acid; D015126:8,11,14-Eicosatrienoic Acid; D013936:Thymidine