Eicosapentaenoic acid is converted to epoxyeicosatetraenoic acids (EpETEs) by several cytochrome P450 isoforms. The major product of this epoxygenase pathway, (±)17(18)-EpETE , relaxes vascular and airway smooth muscle by activating large conductance Ca2+-activated K+ (BKCa) channels by directly interacting with BKα channel subunits. (±)8(9)-EpETE is an epoxygenase pathway product produced from EPA by CYP450 both in vitro and in vivo. The biological actions and physiological effects of this epoxide remain to be determined.