Epoxyeicosatrienoic acids increase intracellular calcium concentration in vascular smooth muscle cells

Epoxyeicosatrienoic acids (EETs) are cytochrome P450-derived metabolites of arachidonic acid. They are potent endogenous vasodilator compounds produced by vascular cells, and EET-induced vasodilation has been attributed to activation of vascular smooth muscle cell (SMC) K⁺ channels. However, in some cells, EETs activate Ca²⁺ channels, resulting in Ca²⁺ influx and increased intracellular Ca²⁺ concentration ([Ca²⁺](i)). We investigated whether EETs also can activate Ca²⁺ channels in vascular SMC and whether the resultant Ca²⁺ influx can influence vascular tone. The 4 EET regioisomers (1 μmol/L) increased-porcine aortic SMC [Ca²⁺](i) by 52% to 81%, whereas arachidonic acid, dihydroxyeicosatrienoic acids, and 15- hydroxyeicosatetraenoic acid (1 μmol/L) produced little effect. The increases in [Ca²⁺](i) produced by 14,15-EET were abolished by removal of extracellular Ca²⁺ and by pretreatment with verapamil (10 μmol/L), an inhibitor of voltage-dependent (L-type) Ca²⁺ channels. 14,15-EET did not alter Ca²⁺ signaling induced by norepinephrine and thapsigargin. When administered to porcine coronary artery rings precontracted with a thromboxane mimetic, 14,15-EET produced relaxation. However, when administered to rings precontracted with acetylcholine or KCl, 14,15-EET produced additional contractions. In rings exposed to 10 mmol/L KCl, a concentration that did not affect resting ring tension, 14,15-EET produced small contractions that were abolished by EGTA (3 mmol/L) or verapamil (10 μmol/L). These observations indicate that 14,15-EET enhances [Ca²⁺](i) influx in vascular SMC through voltage-dependent Ca²⁺ channels. This 14,15- EET-induced increase in [Ca(i)²⁺] can produce vasoconstriction and therefore may act to modulate EET-induced vasorelaxation.