Fig. 2

The application of low concentrations of 20:4-NAPE decreased the excitability of DRG neurons, while higher concentration evoked the opposite effect. (A) A native measurement of changes in the intracellular Ca²⁺ concentration in single neurons under control conditions was conducted during repeated application of KCl (30 mM, 2 s) at 2 min intervals (black line). The application of 100 nM 20:4-NAPE (6 min, green line) decreased the amplitude of the Ca²⁺ transient (340/380). The application of a high 10 µM concentration of 20:4-NAPE (6 min, red line) increased the amplitude. Capsaicin (0.5 µM, 3 s) applied at the end of the experiment evoked robust response. (B) Repeated application of KCl resulted in a slight inhibition of K⁺-induced Ca²⁺ responses in DRG neurons (n = 211). The concentration-dependent effect of 20:4-NAPE application (6 min) on the control K⁺-induced Ca²⁺ responses was evaluated in a range of concentrations, comprising 10 nM (n = 288, p < 0.01 at the 4th min), 100 nM (n = 206, p < 0.001 at the 2nd, 4th and 6th min), 1 µM (n = 269, p < 0.001 at the 2nd, 4th and 6th min), and 10 µM (n = 211, p < 0.001 at 2nd, 4th and 6th min). Statistical significance is shown relative to the Control (black line). (C) A representation of the dual effect induced by 20:4-NAPE at the 4th min. A statistically significant difference was detected in the inhibitory and excitatory effects induced by various concentrations of 20:4-NAPE compared to the Control (black). All cells analysed are depicted. One-way ANOVA (Dunnett’s test) was used for statistical analysis, with criteria for significance ∗∗p < 0.01, ∗∗∗p < 0.001.