title: Activity-dependent heteromerization of the hyperpolarization-activated, cyclic-nucleotide gated (HCN) channels: role of N-linked glycosylation.
abstract: Formation of heteromeric complexes of ion channels via co-assembly of different subunit isoforms provides an important mechanism for enhanced channel diversity. We have previously demonstrated co-association of the hyperpolarization activated cyclic-nucleotide gated (HCN1/HCN2) channel isoforms that was regulated by network (seizure) activity in developing hippocampus. However, the mechanisms that underlie this augmented expression of heteromeric complexes have remained unknown. Glycosylation of the HCN channels has been implicated in the stabilization and membrane expression of heteromeric HCN1/HCN2 constructs in heterologous systems. Therefore, we used in vivo and in vitro systems to test the hypothesis that activity modifies HCN1/HCN2 heteromerization in neurons by modulating the glycosylation state of the channel molecules. Seizure-like activity (SA) increased HCN1/HCN2 heteromerization in hippocampus in vivo as well as in hippocampal organotypic slice cultures. This activity increased the abundance of glycosylated HCN1 but not HCN2-channel molecules. In addition, glycosylated HCN1 channels were preferentially co-immunoprecipitated with the HCN2 isoforms. Provoking SA in vitro in the presence of the N-linked glycosylation blocker tunicamycin abrogated the activity-dependent increase of HCN1/HCN2 heteromerization. Thus, hippocampal HCN1 molecules have a significantly higher probability of being glycosylated after SA, and this might promote a stable heteromerization with HCN2.
authors.affiliation: Department of Pediatrics, University of California, Irvine, Irvine, California 92697-4475, USA.
authors.forename: Qinqin
authors.initials: Q
authors.lastname: Zha
authors.forename: Amy L
authors.initials: AL
authors.lastname: Brewster
authors.forename: Cristina
authors.initials: C
authors.lastname: Richichi
authors.forename: Roland A
authors.initials: RA
authors.lastname: Bender
authors.forename: Tallie Z
authors.initials: TZ
authors.lastname: Baram
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D006031:Glycosylation / Q000187:drug effects; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D047468:Immunoprecipitation / Q000379:methods; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D007608:Kainic Acid; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000502:physiology*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques / Q000379:methods; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012640:Seizures / Q000139:chemically induced / Q000503:physiopathology; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; C578667:Hcn1 protein, rat; C578712:Hcn2 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D015221:Potassium Channels; D014415:Tunicamycin; D007608:Kainic Acid