SS RBCs have higher basal and stimulated cAMP levels compared with AA RBCs.

Cyclic AMP levels in AA or SS RBCs were measured by enzyme-immunoassay (“Materials and methods”). (A) cAMP levels were measured under basal/unstimulated conditions in AA RBCs (n = 4) and SS RBCs (n = 6). Each dot represents the measured cAMP value in 1 × 10⁸ RBCs from one patient. The horizontal bars represent the average values of the individual patient data points. (B) SS (n = 3) and AA (n = 2) RBCs samples (1 × 10⁸ cells per condition) were treated with 80 μM forskolin (Fsk) for 0, 1, 5, 15, and 30 minutes as indicated. After each treatment condition, the RBCs were lysed, and total cellular cAMP levels were measured.