Figure 5.

Effect of RB-040 and RB-042 on (A) SK1 activity and (B) SK2 activity. Concentration-dependent inhibition of SK activity by RB-040 and RB-042 using 3 μM Sph (SK1) or 10 μM Sph (SK2) and 250 μM ATP. The results are expressed as % of control ± SD (n = 3). The control is 100% and equals activity against Sph alone. RB-040 inhibits SK1 activity with IC₅₀ = 2.2 ± 0.22 μM and SK2 activity with IC₅₀ = 5.2 ± 0.82 μM. RB-042 inhibits SK1 activity with IC₅₀ = 5.3 ± 0.5 μM and SK2 activity with IC₅₀ = 5.0 ± 1.3 μM.⁷