title: Differential regulation of HCN channel isoform expression in thalamic neurons of epileptic and non-epileptic rat strains.
abstract: Hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels represent the molecular substrate of the hyperpolarization-activated inward current (I(h)). Although these channels act as pacemakers for the generation of rhythmic activity in the thalamocortical network during sleep and epilepsy, their developmental profile in the thalamus is not yet fully understood. Here we combined electrophysiological, immunohistochemical, and mathematical modeling techniques to examine HCN gene expression and I(h) properties in thalamocortical relay (TC) neurons of the dorsal part of the lateral geniculate nucleus (dLGN) in an epileptic (WAG/Rij) compared to a non-epileptic (ACI) rat strain. Recordings of TC neurons between postnatal day (P) 7 and P90 in both rat strains revealed that I(h) was characterized by higher current density, more hyperpolarized voltage dependence, faster activation kinetics, and reduced cAMP-sensitivity in epileptic animals. All four HCN channel isoforms (HCN1-4) were detected in dLGN, and quantitative analyses revealed a developmental increase of protein expression of HCN1, HCN2, and HCN4 but a decrease of HCN3. HCN1 was expressed at higher levels in WAG/Rij rats, a finding that was correlated with increased expression of the interacting proteins filamin A (FilA) and tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b). Analysis of a simplified computer model of the thalamic network revealed that the alterations of I(h) found in WAG/Rij rats compensate each other in a way that leaves I(h) availability constant, an effect that ensures unaltered cellular burst activity and thalamic oscillations. These data indicate that during postnatal developmental the hyperpolarizing shift in voltage dependency (resulting in less current availability) is compensated by an increase in current density in WAG/Rij thereby possibly limiting the impact of I(h) on epileptogenesis. Because HCN3 is expressed higher in young versus older animals, HCN3 likely does not contribute to alterations in I(h) in older animals.
authors.affiliation: Institut für Physiologie I, Westfälische Wilhelms-Universität Münster, Robert-Koch-Str. 27a, D-48149 Münster, Germany.
authors.forename: Tatyana
authors.initials: T
authors.lastname: Kanyshkova
authors.forename: Patrick
authors.initials: P
authors.lastname: Meuth
authors.forename: Pawan
authors.initials: P
authors.lastname: Bista
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Liu
authors.forename: Petra
authors.initials: P
authors.lastname: Ehling
authors.forename: Luigi
authors.initials: L
authors.lastname: Caputi
authors.forename: Michael
authors.initials: M
authors.lastname: Doengi
authors.forename: Dane M
authors.initials: DM
authors.lastname: Chetkovich
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Pape
authors.forename: Thomas
authors.initials: T
authors.lastname: Budde
mesh_terms: D000818:Animals; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000378:metabolism*; D004827:Epilepsy / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D015870:Gene Expression; D005829:Geniculate Bodies / Q000378:metabolism* / Q000503:physiopathology; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D013045:Species Specificity
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels