Adenosine directly increases erythrocyte SphK1 activity. SphK1 activity in cultured primary erythrocytes from (A) normal human subjects, (B) SCD transgenic mice, and (C) SCD patients after NECA (10 μM) treatment of 30 min. Values shown represent the mean ± SEM (n = 5 for SCD patients and normal human subjects; n = 6 for SCD transgenic mice and WT mice). *P < .05 NECA vs control.