A new mechanism regulating plasma membrane expression of Cav3.2 T-type calcium channels: implication in childhood absence epilepsy

A new mechanism regulating plasma membrane expression of Cav3.2 T-type calcium channels: implication in childhood absence epilepsy T-type calcium channel genes are susceptibility loci in Childhood Absence Epilepsy (CAE). In CAE, several single nucleotide polymorphisms (SNPs) were identified in the gene encoding the Cav3.2 subunit. It was hypothesized that these SNPs may lead to enhanced T-channel activity that would predispose the thalamocortical circuit to oscillate and trigger absence seizures. Electrophysiological studies have identified minor changes in the electrophysiological properties of these Cav3.2 SNPs, unable to support a gain of T-channel activity. Extracellularly hemagglutinin-tagged Cav3.2 channels harbouring CAE mutations were expressed into HEK-293 cells and studied for their membrane expression using a luminometric assay. We have identified that all the CAE SNPs tested significantly enhanced the amount of Cav3.2 channels at the plasma membrane. Since most of the CAE mutations are located within the intracellular loop that connects domain I and domain II, we have hypothesised that the I-II loop participates to the Cav3.2 channel dynamics. Various deletions of the I-II loop were engineered and we have demonstrated that the central region of the I-II loop regulates Cav3.2 surface expression. These results provide novel insights into how CACNA1H SNPs/mutations may contribute to the development of absence epilepsy, and establish the I-II loop as an important regulator of T-channel function and expression.