Gating effects of a Cav2.3 calcium channel mutation linked to developmental and epileptic encephalopathy

Abstract

Developmental and epileptic encephalopathies (DEEs) are a group of neurological disorders primarily affecting young children and are characterized by severe seizures. DEEs are challenging to manage, with some patients experiencing severe side effects or not responding to frontline therapies. This is partly because of the many underlying mechanisms involved in DEE pathology and the relatively limited mechanism-specific action of current treatments. The CACNA1E gene, which encodes the voltage-gated calcium channel Cav2.3 (R-type), has recently been associated with DEEs. More than fifteen different mutations in CACNA1E have been identified in patients with DEEs; however, the mechanisms by which these mutations affect channel function and, thus, their relationship to DEEs, remain largely unknown. Previous research has begun to characterize the functional effects of R-type channel mutations on channel biophysics, but only a handful of mutations have been studied functionally to date. Here, we transiently expressed Cav2.3 channels and used whole-cell patch-clamp to examine the biophysics of one specific disease-associated R-type channel mutant in which leucine 228 is substituted with a proline (L228P). Compared to wild-type, the L228P mutant did not alter peak current density, inactivation kinetics, or recovery from inactivation, but showed a significant shift towards hyperpolarized voltages in both voltage-dependent activation and steady-state inactivation. This resulted in a broader window current shifted towards more hyperpolarized potentials, which predicts increased channel availability and activity at subthreshold voltages relative to wild-type channels. Our results contribute to the ongoing characterization of R-type mutants, with the long-term goal of informing mechanism-specific therapies for DEEs.