Eicosapentaenoic acid (EPA), but not its metabolites (docosapentaenoic acid and docosahexaenoic acid), stimulated nitric oxide (NO) production in endothelial cells in situ and induced endothelium-dependent relaxation of bovine coronary arteries precontracted with U46619. EPA induced a greater production of NO, but a much smaller and more transient elevation of intracellular Ca(2+) concentration ([Ca(2+)]i), than did a Ca(2+) ionophore (ionomycin). EPA stimulated NO production even in endothelial cells in situ loaded with a cytosolic Ca(2+) chelator 1,2-bis-o-aminophenoxythamine-N',N',N'-tetraacetic acid, which abolished the [Ca(2+)]i elevations induced by ATP and EPA. The EPA-induced vasorelaxation was inhibited by N(omega)-nitro-L-arginine methyl ester. Immunostaining analysis of endothelial NO synthase (eNOS) and caveolin-1 in cultured endothelial cells revealed eNOS to be colocalized with caveolin in the cell membrane at a resting state, while EPA stimulated the translocation of eNOS to the cytosol and its dissociation from caveolin, to an extent comparable to that of the eNOS translocation induced by a [Ca(2+)]i-elevating agonist (10 microM bradykinin). Thus, EPA induces Ca(2+)-independent activation and translocation of eNOS and endothelium-dependent vasorelaxation.