Potentiation of Ca2+ signaling in endothelial cells by 11,12-epoxyeicosatrienoic acid

Incubation of endothelium with an increased epoxyeicosatrienoic acid (EET) concentration specifically augments the endothelium-dependent relaxation as cribed to endothelium-derived hyperpolarizing factor in porcine coronary ar teries (Weintraub et al., Circ Res 1997;81:258-267). Experiments were desig ned to test whether such sustained increased levels of EETs in the environm ent of endothelial cells alters Ca2+ signaling. Changes in cytosolic Ca2+ w ere monitored in cultured porcine aortic endothelial cells (PAECs) and in t he human endothelial EA.hy926 cell line after incubation (or not) with 5 mu M 11,12-epoxyeicosatrienoic acid (EET). Although the mobilization of intra cellular Ca2+ induced by 2 mu M thapsigargin was not affected significantly , EET treatment augmented the capacitative Ca2+ entry evoked by the Ca2+-AT Pase) inhibitor in both cell types. Similar observations were obtained by u sing histamine as a stimulant in EA.hy926 cells. As assessed in PAECs, 2 mu g/ml triacsin C, a known inhibitor of the incorporation of EETs into phosp holipids, did not significantly affect the potentiating action of EETs on C a2+ signaling in response to thapsigargin. However, in solvent-control cell s, triacsin C significantly reduced both the mobilization of Ca2+ from intr acellular stores and the capacitative Ca2+ entry provoked by thapsigargin. Thus the EET-potentiating effect overcomes the inhibitory action of triacsi n C on Ca2+ signaling in endothelial cells. Taken together, these results d emonstrate that sustained increases in EETs may amplify Ca2+ signaling. How ever, contrary to the EET-induced augmentation of endothelium-dependent rel axation in the porcine coronary artery, resistance of this novel action of EETs to triacsin C suggests that the mechanism involved does not depend on incorporation into phospholipids.