T he molecular defect in sickle cell disease resides in the beta globin gene, with consequent defects in erythrocytes only, suggesting that the vascular occlusion and vasomotor instability which characterize this disease are the result of interactions between abnormal sickle erythrocytes and cells of the blood vessel wall. We explored whether sickle erythrocytes may have effects on vascular tone, exclusive of adhesion events. Exposure of human endothelial cells in culture to previously sickled sickle erythrocytes resulted in a four to eight-fold transcriptional induction of the gene encoding the potent vasoconstrictor endothelin-1 (ET-1). Unsickled sickle erythrocytes or normal erythrocytes exposed to "sickling" conditions had no effect on ET-1 gene induction. Contact of the sickled erythrocytes with the endothelium was not required. Elevations in the ET-1 transcript peaked at 3 h after exposure and persisted for up to 24 h. Four to sixfold increases in the amount of ET-1 peptide was released into the medium surrounding the endothelial cells after exposure to sickled sickle erythrocytes. This is the first demonstration of the regulation of gene expression in endothelial cells as a result of interaction with sickle cells, with induction of genes encoding vasoconstrictors. Furthermore, these findings suggest that sickle erythrocytes may have the capacity to affect local vasomotor tone directly.