Gating Effects of Mutations in the Cav3.2 T-type Calcium Channel Associated with Childhood Absence Epilepsy

Childhood absence epilepsy (CAE) is a type of generalized epilepsy observed in 2–10% of epileptic children. In a recent study by Chen et al. (Chen, Y., Lu, J., Pan, H., Zhang, Y., Wu, H., Xu, K., Liu, X., Jiang, Y., Bao, X., Yao, Z., Ding, K., Lo, W. H., Qiang, B., Chan, P., Shen, Y., and Wu, X. (2003) Ann. Neurol. 54, 239–243) 12 missense mutations were identified in the CACNA1H (Cav3.2) gene in 14 of 118 patients with CAE but not in 230 control individuals. We have functionally characterized five of these mutations (F161L, E282K, C456S, V831M, and D1463N) using rat Cav3.2 and whole-cell patch clamp recordings in transfected HEK293 cells. Two of the mutations, F161L and E282K, mediated an ∼10-mV hyperpolarizing shift in the half-activation potential. Mutation V831M caused a ∼50% slowing of inactivation relative to control and shifted half-inactivation potential ∼10 mV toward more depolarized potentials. Mean time to peak was significantly increased by mutation V831M but was unchanged for all others. No resolvable changes in the parameters of the IV relation or current kinetics were observed with the remaining mutations. The findings suggest that several of the Cav3.2 mutants allow for greater calcium influx during physiological activation and in the case of F161L and E282K can result in channel openings at more hyperpolarized (close to resting) potentials. This may underlie the propensity for seizures in patients with CAE.