Figure 5.

Potential role of ClC-2 in epilepsy. A, Two-electrode voltage-clamp analysis of Xenopus oocytes previously injected with 10 ng of WT ClC-2 cRNA (■) or with a construct modeled on the truncating Gins597 mutation (○) from a family with epilepsy (Haug et al., 2003). Injecting half the amount (5 ng) of WT ClC-2 cRNA gave about half the current amplitude (□). Coinjection of 5 ng of WT and 5 ng of Gins597 cRNA (•) yielded similar current amplitudes, indicating that the mutant lacks a dominant-negative effect. Currents were obtained from >15 oocytes from three batches, averaged, and normalized to wild type. B, Two-electrode voltage-clamp analysis of two sequence variants identified in epileptic patients (D'Agostino et al., 2004) in the present screen of patients with leukodystrophy and by Stogmann et al. (2006). Currents from ClC-2_E718D (▾; n = 21 oocytes) and ClC-2_R688Q (○; n = 23) were indistinguishable from WT ClC-2 currents (■; n = 19). Averaged and normalized currents from three batches of oocytes are shown. C, D, Seizure susceptibility of WT, Clcn2 ^+/− (HET), and Clcn2 ^−/− (KO) mice as determined by exposure to fluorethyl (applied at 10 ml/min to the chamber; C) or pentylenetetrazol (PTZ; injected at 50 mg/kg body weight; D). C, The apparent slight decrease in threshold in Clcn2 ^−/− mice (2.34 ± 0.13 min; n = 8 mice) was not statistically different (p = 0.072) from those of WT (2.95 ± 0.25; n = 12) or Clcn2 ^+/− mice (2.91 ± 0.21 min; n = 3). D, There was no difference between seizure thresholds of WT and KO animals on exposure to PTZ (3.70 ± 1.41 vs 4.04 ± 1.25 min; n = 6 mice each). Error bars indicate SEM.