Fig. 2.

IM increase tetrodotoxin-resistant voltage-gated Na⁺ current (TTX-R I_Na) in dural afferents from male rats. Na⁺ current was evoked in dural afferents before (Pre-IM) and after (Post-IM) IM application. A voltage protocol was used to isolate TTX-R I_Na from tetrodotoxin-sensitive (TTX-S) I_Na as described in materials and methods. A significant increase in current was detected in 13 of 14 afferents studied and was associated with a ∼25% increase in conductance (G). Conductance-voltage (G-V) data from each neuron tested were normalized to the maximal conductance determined before IM application (G_max-Baseline) and pooled. Data points between −60 and −45 mV are omitted to facilitate comparisons between Pre- and Post-IM. Pooled data are fitted with a Boltzmann equation with values for potential for half-maximal activation (V_0.5) of −2.9 ± 0.3 and −5.8 ± 1.3 and slope of 4.5 ± 0.6 and 3.8 ± 0.7 for Pre- and Post-IM, respectively. Inset, typical TTX-R I_Na evoked in dural afferents from male rats before (Baseline) and 90 s after (IM) the IM application.