Epoxyeicosatrienoic acids activate Na+/H+ exchange and are mitogenic in cultured rat glomerular mesangial cells

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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 < 0.025; 10−6 M 14, 15‐EET: 145 ± 10%; n = 20; P < 0.0005; 10−6 M 8,9‐EET: 167 ± 31%; n = 9; P < 0.05), which was not affected by addition of the cyclooxygenase inhibitor indon ethacin. 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, > 85% of 3 mM 22Na uptake into mesangial cells was inhibited by I 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, > 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.

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