Epinephrine modulates SS RBC adhesion to ECs. Adhesion of SS and normal RBCs to both EC-RF24 cells (A) and HUVECs (B-D) was tested, and results are presented as percent of cells adherent at a shear stress of 2 dynes/cm². (A) SS RBCs were sham treated or stimulated with 20 nM epinephrine for 1 to 15 minutes. (B) SS RBCs were sham treated, activated with 20 nM epinephrine for 1 minute, or preincubated with 30 nM PKAI, washed, and then activated with 20 nM epinephrine for 1 minute prior to adhesion assays (n = 3). As a control, HUVECs were incubated with the supernatant obtained from the last wash of SS RBC treatment with 20 nM epinephrine for 1 minute (n = 3), washed, and then tested for their ability to support adhesion of nontreated SS RBCs. (C) Normal RBCs were sham treated or activated with 20 nM epinephrine (1 minute) and then used for adhesion assays (n = 3). (D) Separation of reticulocytes and mature RBCs was accomplished using antitransferrin receptor mAb 5E9 and goat anti–mouse IgG–coated magnetic microbeads as described in “Materials and methods.” Adhesion assays to HUVECs were then performed after incubation of unselected SS RBCs, mature SS RBCs, or SS reticulocytes with 20 nM epinephrine for 1 minute. In panels B-D, error bars show SD of 3 different experiments measuring adhesion at a shear stress of 2 dynes/cm².