Up-regulation of endogenous cAMP induces SS RBC adhesion to EC-RF24 cells through a PKA-dependent pathway. (A) SS RBCs were sham treated or treated with Pertussis toxin (0.5 μg/mL, black symbols; 1 μg/mL, white symbols; 2 μg/mL, gray symbols) and tested for adhesion at a shear stress of 2 dynes/cm2. All 3 patients were tested once for adhesion. SS RBCs from each patient were treated with the 3 different concentrations of Pertussis toxin. (B) Adhesion of sham-treated, forskolin-treated (80 μM), or forskolin + IBMX (0.2 mM)–treated SS RBCs was compared (n = 3). (C) Inhibition by PKAI of adhesion of SS RBCs activated with 0.2 mM IBMX + 176 μM db-cAMP was assayed at a shear stress of 2 dynes/cm2. Results are presented as percent inhibition of IBMX + db-cAMP–stimulated SS RBC adhesion (n = 3). Black bar: inhibitory effect of 30 nM PKAI present at the same time as stimulatory agents. White bar: effect of pretreatment of SS RBCs with 30 nM PKAI, followed by washing and treatment with IBMX and db-cAMP. (D) SS RBCs were sham treated or treated with 0.2 mM IBMX + 80 μM forskolin, 15 nM okadeic acid, 0.2 mM IBMX + 80 μM forskolin + 15 nM okadeic acid, or okadeic acid + PKAI (30 nM). Adhesion to EC-RF24 cells was assayed at a shear stress of 1 dyne/cm2. In panels B and C, error bars show SD.
