Representative traces illustrating the effect of cer (10 μm), sph (10 μm), and SPP (5 μm) on DiBAC₄ fluorescence in cultured rat OLGs. An increase in fluorescence intensity indicates depolarization.A, Cer-induced depolarization and sph-induced hyperpolarization. Note that 0.1% ethanol (EtOH) and 0.1% DMSO had no effect on OLG RMP. B, SPP-induced depolarization and sph-induced hyperpolarization compared with depolarization induced by high K⁺ (70 mm). C, Effect of sph in the presence of PMA (320 nm). D, Effect of sph and cer in Ca²⁺-free conditions.