title: An N-terminal deletion variant of HCN1 in the epileptic WAG/Rij strain modulates HCN current densities.
abstract: Rats of the Wistar Albino Glaxo/Rij (WAG/Rij) strain show symptoms resembling human absence epilepsy. Thalamocortical neurons of WAG/Rij rats are characterized by an increased HCN1 expression, a negative shift in I h activation curve, and an altered responsiveness of I h to cAMP. We cloned HCN1 channels from rat thalamic cDNA libraries of the WAG/Rij strain and found an N-terminal deletion of 37 amino acids. In addition, WAG-HCN1 has a stretch of six amino acids, directly following the deletion, where the wild-type sequence (GNSVCF) is changed to a polyserine motif. These alterations were found solely in thalamus mRNA but not in genomic DNA. The truncated WAG-HCN1 was detected late postnatal in WAG/Rij rats and was not passed on to rats obtained from pairing WAG/Rij and non-epileptic August Copenhagen Irish rats. Heterologous expression in Xenopus oocytes revealed 2.2-fold increased current amplitude of WAG-HCN1 compared to rat HCN1. While WAG-HCN1 channels did not have altered current kinetics or changed regulation by protein kinases, fluorescence imaging revealed a faster and more pronounced surface expression of WAG-HCN1. Using co-expression experiments, we found that WAG-HCN1 channels suppress heteromeric HCN2 and HCN4 currents. Moreover, heteromeric channels of WAG-HCN1 with HCN2 have a reduced cAMP sensitivity. Functional studies revealed that the gain-of-function of WAG-HCN1 is not caused by the N-terminal deletion alone, thus requiring a change of the N-terminal GNSVCF motif. Our findings may help to explain previous observations in neurons of the WAG/Rij strain and indicate that WAG-HCN1 may contribute to the genesis of absence seizures in WAG/Rij rats.
authors.affiliation: Institute for Physiology and Pathophysiology, Vegetative Physiology, Philipps-University of Marburg Marburg, Germany.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Wemhöner
authors.affiliation: Institute for Physiology I, Westfälische Wilhelms-Universität Münster, Germany.
authors.forename: Tatyana
authors.initials: T
authors.lastname: Kanyshkova
authors.affiliation: Institute for Physiology and Pathophysiology, Vegetative Physiology, Philipps-University of Marburg Marburg, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Silbernagel
authors.affiliation: Department of Neurology, Westfälische Wilhelms-Universität Münster, Germany.
authors.forename: Juncal
authors.initials: J
authors.lastname: Fernandez-Orth
authors.affiliation: Department of Neurology, University Medical Center, Johannes Gutenberg-University Mainz Mainz, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bittner
authors.affiliation: Institute for Physiology and Pathophysiology, Vegetative Physiology, Philipps-University of Marburg Marburg, Germany.
authors.forename: Aytug K
authors.initials: AK
authors.lastname: Kiper
authors.affiliation: Institute for Physiology and Pathophysiology, Vegetative Physiology, Philipps-University of Marburg Marburg, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Rinné
authors.affiliation: Institute for Physiology and Pathophysiology, Vegetative Physiology, Philipps-University of Marburg Marburg, Germany.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Netter
authors.affiliation: Department of Neurology, Westfälische Wilhelms-Universität Münster, Germany.
authors.forename: Sven G
authors.initials: SG
authors.lastname: Meuth
authors.affiliation: Institute for Physiology I, Westfälische Wilhelms-Universität Münster, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Budde
authors.affiliation: Institute for Physiology and Pathophysiology, Vegetative Physiology, Philipps-University of Marburg Marburg, Germany.
authors.forename: Niels
authors.initials: N
authors.lastname: Decher
keywords: HCN; Ih; WAG/Rij rat; absence epilepsy; thalamocortical relay neurons