Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), originally identified as the major receptor for oxidized low-density lipoprotein in endothelial cells, mediates the interaction between activated platelets and endothelial cells. Stimulation of LOX-1 causes various functional changes in endothelial cells relevant to 'endothelial dysfunction'. This study investigated the cellular responses to platelet binding via LOX-1, comparing it with CD40, which also mediates platelet-binding in endothelial cells. Activated platelets, which bind both LOX-1 and CD40, induced endothelin-1 production via co-operation of LOX-1 and CD40. Stimulation of LOX-1 by oxidized low-density lipoprotein induced the expression of CD40 as well as LOX-1 itself, and stimulation of CD40 by CD40L induced the expression of LOX-1 as well as CD40. Activated platelets induced both LOX-1 and CD40 expression via these two systems in endothelial cells. Application of superoxide dismutase suppressed LOX-1-mediated, but not CD40-mediated, induction of endothelin-1. LOX-1 and CD40 synergistically, but through a distinct pathway, work to induce endothelin-1 expression in endothelial cells. This co-operative action between LOX-1 and CD40 might play a key role in the induction of endothelial dysfunction.