Figure 3.

Ionic nature of the excitatory currents induced by S1P. A, Typical recording of a responsive neuron after a short pulse of S1P (1 μm, 10 s). B, The graph shows the dose–response relationship of the S1P-induced conductance. The EC₅₀ was 0.160 μm S1P. C, Top, Representative Ca²⁺ imaging measurement of the S1P-evoked Ca²⁺ transient in DRG neurons in ECS (containing 2 mm Ca²⁺). Bottom, The Ca²⁺ rise induced by S1P was completely abolished in Ca²⁺ free condition (5 mm EGTA, ∼3.5 min exposure) but lightly recovered after washout (2 min). D, E, A small change in [Ca²⁺]_i induced by short application of S1P (1 μm, 60 s) was observed in most DRG neurons. In presence of TG (1 μm, 5 min), the percentage of S1P-responding neurons and the Ca²⁺ increase magnitude was not significantly different from control conditions. For each Ca²⁺ measurement, 25–30 neurons (N ≥ 3 mice) were randomly selected in the field. F, Top, Whole-cell recording from S1P-activated current in “cation free” condition (0 Ca²⁺, 0 K⁺, 0 Na⁺, 1 min). Bottom, Quantification of the S1P-induced current density for recordings in F that remained unaltered after neuron exposure to “cation free” solution (3 min after S1P application). n.s., Not significant (p > 0.05). ***p < 0.001.