Abstract

Nerve excitability studies were performed on rat saphenous skin-nerve preparations in vitro. VGSC blockers lidocaine, carbamazepine (CBZ) and lacosamide were dissolved in synthetic interstitial fluid at 1, 3, 10, 30 and 100 μM. Measurements were performed before and after perfusion for 20 min. Drug responses were compared with baseline values using student's paired and unpaired t-tests for within and between group analyses. Lidocaine had reversible dose-dependent effects on all excitability parameters. Strength duration time constant (SDTC), depolarising threshold electrotonus (TEd) and superexcitability (SX) were all decreased and the I/V curve was shifted towards outward rectification. TEd was the most sensitive parameter with effects seen at concentrations as low as 1 μM (N=8 df=7, t=2.4, p=0.05), indicating use-dependent blockade of VGSCs. Significant differences in SDTC (N=9, df=8, t=3.66, p=0.006) and SX (N=8, df=7, t=−3.48, p=0.01) required concentrations greater than 10 μM. CBZ had qualitatively similar effects but with less efficacy. Lacosamide showed a different pattern with less effects on TEd and an increase in SX, peaking at 30 μM (N=5, df=4, t=4.12, p=0.01). Nerve excitability parameters are sensitive biomarkers for drug activity at VGSCs, capable of discriminating quantitative and qualitative differences between VGSC blockers. They may be used to screen for activity and provide comparative functional information on drug dosing.