Figure 1.

LA selectively inhibits T-type Ca²⁺ currents and underlying after-depolarizing potentials in acutely dissociated rat sensory neurons. A, Traces of T-current in a representative DRG cell before and after (black traces), as well as during bath application of 1 mm LA (gray trace), which reversibly inhibited ∼38% of peak inward current. Bars indicate calibration. B, Temporal record from the same cell presented on panel A of this figure. Gray bar indicates duration of LA application. C, Concentration-response relationship for LA inhibition of T-current in rat DRG cells (n = 6–20 per data point). Solid line is the best fit (Eq. 1; see Materials and Methods) yielding IC₅₀ of 3.3 ± 1.5 μm, slope coefficient 0.8 ± 0.2, and maximal inhibition of 40.4 ± 3.1% of the peak of T-current. D, Traces of HVA Ca²⁺ current from another DRG cell before (black trace) and during the bath application of 1 mm LA (gray trace). Bars indicate calibration. E, AP waveforms in a representative DRG cell before (black trace) and during application of 100 μm LA (gray trace). Note that LA application had little effect on RMP and the initial AP spike, but attenuated the maximal amplitude of ADP by ∼30% and the duration of ADP (measured at half-maximal height) by ∼45%. F, The same experimental protocol (described in E) was used in another DRG cell that fired a repetitive APs at the crest of ADP (black traces). When 1 mm LA was applied in the bath, the initial amplitude of ADP was decreased ∼20% and the cell did not fire repetitively (gray trace) when the same single depolarizing stimulus was injected through the recording electrode.