FIGURE 1.

Rat erythrocytes take up sphingosine and release sphingosine 1-phosphate. Rat erythrocytes (1.8 × 10⁶ cells) were incubated with [³H]sphingosine for the indicated times at 37 °C. Then the assay buffer and erythrocytes were separated by centrifugation. The amounts of S1P in the assay buffer (A, extracellular) and erythrocytes (B, intracellular) were determined as described under “Experimental Procedures.” Closed and open circles indicate sphingosine (Sph) and S1P, respectively. The total amounts of sphingosine and S1P at 0.2 min were set at 100%. Experiments were performed more than three times, and the error bars indicate the S.D.