Hippocampal Seizure Resistance and Reduced Neuronal Excitotoxicity in Mice Lacking the Ca_v2.3 E/R-Type Voltage-Gated Calcium Channel

Abstract

Voltage-gated calcium channels are key components in the etiology and pathogenesis of epilepsies. Former studies mainly focused on P/Q-type Ca(v)2.1 and T-type Ca(v)3.2 Ca(2+) channels involved in absence epileptogenesis, but recent findings also point to an intriguing role of the Ca(v)2.3 E/R-type Ca(2+) channel in ictogenesis and seizure propagation. Based on the observation that Ca(v)2.3 is thought to induce plateau potentials in CA1 pyramidal cells, which can trigger epileptiform activity, our recent investigation revealed reduced PTZ-seizure susceptibility and altered seizure architecture in Ca(v)2.3(-/-) mice compared with controls. In the present study we tested hippocampal seizure susceptibility in Ca(v)2.3-deficient mice using surface and deep intrahippocampal telemetric EEG recordings as well as phenotypic seizure video analysis. Administration of kainic acid (30 mg/kg ip) revealed clear alteration in behavioral seizure architecture and dramatic resistance to limbic seizures in Ca(v)2.3(-/-) mice compared with controls, whereas no difference in hippocampal EEG seizure activity between both genotypes could be detected at this suprathreshold dosage. The same tendency was observed for NMDA seizure susceptibility (150 mg/kg ip) approaching the level of significance. In addition, histochemical analysis within the hippocampus revealed that excitotoxic effects after kainic acid administration are absent in Ca(v)2.3(-/-) mice, whereas Ca(v)2.3(+/+) animals exhibited clear and typical signs of excitotoxic cell death. These findings clearly indicate that the Ca(v)2.3 voltage-gated calcium channel plays a crucial role in both hippocampal ictogenesis and seizure generalization and is of central importance in neuronal degeneration after excitotoxic events.

The Role of Calcium Channels in Epilepsy

“…The roles, if any, played by other calcium channel subtypes in epileptogenesis await elucidation. Ca V 2.3 (R-type) channels in the thalamus have been implicated in burst firing and potentially proictogenic "plateau potentials" (Randall and Tsien 1997;Metz et al 2005;Zaman et al 2011) with Ca V 2.3 null mice showing an altered susceptibility to absence seizures, as well as resistance to pharmacologically induced limbic seizures, convulsions, and excitotoxic cell death (Weiergraber et al 2006(Weiergraber et al , 2007(Weiergraber et al , 2008, tantalizing data that require further study.…”

Interaction of recombinant and native Cav2.3 E-/R-type voltage-gated Ca2+ channels with the molecular chaperone Hsp70

“…9 Under similar conditions, the II-III loop of the human Ca v 2.2 (N-type) Ca 2+ channel also immunoprecipitated with myc-tagged Hsp70 ( Figure 1A, lane 3). However, no specific immunoprecipitation was observed with the C-terminus of Ca v 2.3 ( Figure 1A, lane 5 vs lane 7), although sufficient Hsp70 protein was expressed (compare supernatants from both batches, Figure 1A, lane 6 vs lane 8), assuming that the cytosolic II-III linkers rather than the C-terminus may be a common target for membrane-bound Hsp70, at least for human E-/R-type and N-type voltage-gated Ca 2+ channels. In previous studies, 15-deoxyspergualin, the synthetic analog of spergualin, was used in a retina model to test its functional effects on E-/R-type channel-mediated gamma aminobutyric acid release.…”

“…Furthermore, histochemical analysis within the hippocampus revealed excitotoxic effects after kainate administration only for Ca v 2.3 controls but not for Ca v 2.3-deficient mice. 8 Because Hsp70 was identified as a tightly bound interaction partner of Ca v 2.3, 9 similar kainate injection experiments were repeated at 20 mg/ kg instead of 30 mg/kg 8 to reduce the number of mice reaching a stage of maximum generalized seizure activity and to keep a sufficient number of control mice alive. Hsp70 expression was compared for both genotypes before and after kainate injection.…”

“…Ten different genes encoding the ion-conducting α1-subunits of voltage-gated Ca 7,8 To understand the molecular mechanism of protection from kainate-induced neurodegeneration, we screened for protein interaction partners which may be putative candidates within a signaling pathway for selective hippocampal cell death. Using channel protein segments facing the cytosolic compartment, a biochemical approach demonstrated that the molecular chaperone, heat shock 70 kDa protein 1A (Hsp70), was tightly bound to the recombinant II-III loop when overexpressed in HEK-293 cells.…”

The role of ion channels and intracellular metal ions in apoptosis of Xenopus oocytes

“…Hippocampal cells (mice) Kainic acid-induced exitoxicity, EFCH1 overexpression (Suzuki et al, 2004;Weiergräber et al, 2007) Anion channels VDAC Hippocampal cells (mouse and rat) STS (Akanda et al, 2008;Elinder et al, 2005) The X. laevis oocyte as a model system…”