Figure 9.

Ligand-independent and ligand-dependent inhibition of Cav channels in DRG neurons from mice with latent sensitization. Mice were injected in one hindpaw with 5 μl of saline or CFA. DRG neurons (L4–L5) were acutely isolated from the saline-injected or the CFA-injected mice after day 21. A, Whole-cell patch-clamp recordings were used to measure Cav currents evoked by a two-pulse protocol (bottom traces). P2 includes a high voltage prepulse from −80 mV to +80 mV to dissociate Gβγ subunits from the Cav channels, whereas P1 consists only of a test pulse from −80 mV to +10 mV. Constitutive inhibition of the Cav channels was indicated by a larger current with the P2 protocol (red traces) resulting in an increase in the P2/P1 ratio. B, P1/P2 ratio obtained from DRG of saline-injected and CFA-injected mice in the absence and presence of NTX (1 μm). Two-way ANOVA: NTX p = 0.023, CFA p = 0.15, interaction p = 0.0497. Holm-Sidak's post hoc tests: **p < 0.01 compared with baseline, †p < 0.05 as shown. C, P1/P2 ratio obtained from DRG of CFA-injected mice untreated (baseline) or in presence of NTX (1 μm), 6β-naltrexol (10 μm), and NTX plus 6β-naltrexol. One-way ANOVA: p < 0.0001. D, DAMGO was used to assess MOR ligand inhibition of Cav currents in saline-injected mice and mice with CFA-induced latent sensitization. A single depolarizing 100 ms pulse from −70 mV to +10 mV was used to evoke Cav currents. An exemplar recording shows the following: (1) the basal Cav current (initial), (2) DAMGO (1 μm) inhibition of Cav current, and (3) the current after DAMGO had been washed off. E, DAMGO inhibition of Cav currents expressed as a percentage of the total current in neurons from the ipsilateral L4–L6 DRG from CFA- and saline-injected mice; there was no effect of CFA. Holm-Sidak's post hoc tests: *p < 0.05 compared with baseline; ††p < 0.01, †††p < 0.001 compared with NTX. Numbers indicate the number of neurons recorded in each group (n).