Mechanisms of epinephrine-stimulated adhesion in SS RBCs from the responsive patient subpopulation.
Adhesion of SS RBCs to immobilized laminin was measured in the flow adhesion assay (“Materials and methods”) under basal conditions, following epinephrine stimulation (1 × 10−2 μM epinephrine for 1 minute), or in the presence of one of the inhibitors described in B, C, and D. (A) Baseline adhesion is set at 1 (solid line), and the log of the fold change from basal adhesion following epinephrine stimulation is indicated on the y-axis. Patients with more than 1.5-fold (50%) elevation in adhesion (on or above dotted line) were classified as responders, and patients below the dotted line were classified as nonresponders. Each dot represents a separate patient (n = 28). Inhibition of epinephrine-stimulated adhesion was measured in the presence of (B) the nonspecific β-AR antagonist propranolol (170 μM for 30 minutes) or the β2-specific AR antagonist butoxamine (160 μM for 30 minutes (P < .05, n = 5), (C) a PKA inhibitor (PKAI) (36 nM for 1 hour) (P < .05, n = 4), or (D) 100 μg/mL soluble BCAM/Lu (solid line) or 100 μg/mL soluble VCAM (control) (dotted line). The portion of adhesion stimulated by epinephrine was inhibited by an average of 96% (n = 4,P < .05). (The dotted line in C and D indicates basal adhesion normalized to 1).
