Research ReportSeizure susceptibility is associated with altered protein expression of voltage-gated calcium channel subunits in inferior colliculus neurons of the genetically epilepsy-prone rat

The inferior colliculus (IC) is the consensus site for seizure initiation in the genetically epilepsy-prone rat (GEPR). We have previously reported that the current density of high threshold voltage-activated (HVA) calcium (Ca2+) channels was markedly enhanced in IC neurons of the GEPR-3 (moderate seizure severity substrain of the GEPR). The present study examines whether subunit protein levels of HVA Ca2+ channels are altered in IC neurons that exhibit enhanced Ca2+ current density. Quantification shows that the levels of protein expression of the Ca2+ channel pore-forming α1D (L-type) and α1E subunits (R-type) were significantly increased in IC neurons of seizure-naive GEPR-3s (SN-GEPR-3s) compared to control Sprague-Dawley (SD) rats. Significant increases and decreases in the levels of protein expression of Ca2+ channel regulatory β3 and α2δ subunits occurred in IC neurons of SN-GEPR-3s compared to control SD rats, respectively. No changes occurred in the protein expression of Ca2+ channel pore-forming α1A (P/Q-type), α1B (N-type) and α1C (L-type) subunits in IC neurons of SN-GEPR-3s compared to control SD rats. A single seizure selectively enhanced protein expression of Ca2+ channel α1A subunits in IC neurons of GEPR-3s. Thus, up-regulation of Ca2+ channel α1D and α1E subunits may represent the molecular mechanisms for the enhanced current density of L- and R-type of HVA Ca2+ channels in IC neurons of the GEPR, and may contribute to the genetic basis of their enhanced seizure susceptibility. The up-regulation of Ca2+ channel α1A subunits induced by seizures may contribute to the increasing IC neuronal excitability that results from repetitive seizures in the GEPR.