Fig. 2: Intracellular S1P concentration regulates RBC glucose uptake in vivo.
A Intracellular S1P levels and (B) corresponding S1P efflux to BSA in RBC (isolated from mice treated or not with 4-deoxypyridoxine (DOP) for 3 weeks) (control n = 4; DOP n = 9). C Glucose uptake rate of same RBC before and after S1P unloading with BSA (n = 7). D Intracellular S1P levels and (E) corresponding S1P efflux in RBC from Sgpl1vav-cre- and Sgpl1vav-cre+ mice (n = 7). F Glucose uptake of RBC from same mice as in (E) in the presence and absence of BSA for 30 min (n = 7 each). G intracellular S1P levels and (H) corresponding S1P efflux in RBC from SphK1+/+ and SphK1−/− mice incubated with vehicle or 1 µM Sph followed by incubation without or with BSA; inset shows basal intracellular S1P level of SphK1+/+ and SphK1–/– mice (n = 5 each). I Glucose uptake in RBC from SphK1+/+ and SphK1−/− mice treated as in (A) (n = 4/6). J, K sphingosine levels from (G) and (H), n = 5 each. L Glucose uptake rate in mouse RBC loaded with vehicle, 1 μM Sph, 1 μM D, L-threo-dihydrosphingosine, 1 µM N, N-dimethylsphingosine or 1 µM L-threo-sphingosine (n = 4). Data are presented as mean ± sd and tested with stack matched two-way ANOVA followed by a Tukey’s multiple comparison test (A–K; # for comparing vehicle or genotype vs. treatment or genotype; * for comparing treatments) or paired one‐way ANOVA in (L), and a mixed model due to randomly missing values in (K); in (B, E), there is also a significance in the controls with and w/o BSA if a paired t test was used. The use of the stack matched two-way ANOVA emphasizes that more S1P can be extracted from DOP-RBC. ns= not significant; p# < 0.05; p## < 0.01; p#### < 0.0001; p* < 0.05; p** < 0.01; p*** < 0.001; p**** < 0.0001.
