Nitric oxide (NO) generated by endothelial NO synthase (eNOS) is a key regulator of endothelial cell (EC) migration. Whereas the effects of acute NO generation are generally stimulatory, the role of chronic basal NO release has not been explored so far. Here, we addressed this question both in HeLa and in human endothelial cells. In stably transfected HeLa cells, inducibly expressing eNOS, expression of the enzyme per se blunted the phosphorylation of Akt/PKB in response to serum and strongly inhibited chemotaxis, an effect partially blocked by eNOS- and Soluble guanylyl cyclase (sGC) inhibitors. Likewise, long-term pre-treatment of non-transfected HeLa cells with nanomolar concentrations of an NO donor inhibited subsequent migration, an effect blocked by sGC inhibition and mimicked by a cGMP analog. Finally, EC migration was stimulated by chronic pre-treatment with an eNOS inhibitor. Thus, in addition to its well-known stimulatory role, eNOS attenuates migration through basal long-term NO release. (C) 2009 Elsevier Inc. All rights reserved.