['Tobacco abuse is still among the most important cardiovascular risk factors in modern society. We investigated whether sub-chronic nicotine exposure can induce endothelial dysfunction and communication failure.', 'Primary human umbilical vein endothelial cells (HUVEC) were cultured with or without 1 microM nicotine given for the entire cell culture passage until confluence (5+/-0.5 days). Cells were cultured on special Petri dishes consisting of two compartments which communicated only via a small cellular bridge. We determined the propagation of the NO signal after stimulation of compartment A with ATP by simultaneous spectrophotometric measurement of ATP and methemoglobin formation indicating NO release in compartment B. In HUVECs grown under nicotine we found significantly reduced NO formation in compartment B 5 min after ATP stimulation of compartment A. At that time, there was no ATP detectable in compartment B. The difference in NO-signal-propagation could be abolished with the gap junction blocker Na-propionate. Western blot and immunohistochemistry indicated significantly reduced levels of endothelial gap junction proteins Cx37 and Cx43, but not Cx40. Dye transfer experiments revealed reduced number of communicating cells in nicotine exposed cells indicating the functional relevance.'] Does sub-chronic nicotine exposure induce intercellular communication failure and differential down-regulation of connexins in cultured human endothelial cells?