title: HCN1 channel subunits are a molecular substrate for hypnotic actions of ketamine.
abstract: Ketamine has important anesthetic, analgesic, and psychotropic actions. It is widely believed that NMDA receptor inhibition accounts for ketamine actions, but there remains a dearth of behavioral evidence to support this hypothesis. Here, we present an alternative, behaviorally relevant molecular substrate for anesthetic effects of ketamine: the HCN1 pacemaker channels that underlie a neuronal hyperpolarization-activated cationic current (I(h)). Ketamine caused subunit-specific inhibition of recombinant HCN1-containing channels and neuronal I(h) at clinically relevant concentrations; the channels were more potently inhibited by S-(+)-ketamine than racemic ketamine, consistent with anesthetic actions of the compounds. In cortical pyramidal neurons from wild-type, but not HCN1 knock-out mice, ketamine induced membrane hyperpolarization and enhanced dendritosomatic synaptic coupling; both effects are known to promote cortical synchronization and support slow cortical rhythms, like those accompanying anesthetic-induced hypnosis. Accordingly, we found that the potency for ketamine to provoke a loss-of-righting reflex, a behavioral correlate of hypnosis, was strongly reduced in HCN1 knock-out mice. In addition, hypnotic sensitivity to two other intravenous anesthetics in HCN1 knock-out mice matched effects on HCN1 channels; propofol selectively inhibited HCN1 channels and propofol sensitivity was diminished in HCN1 knock-out mice, whereas etomidate had no effect on HCN1 channels and hypnotic sensitivity to etomidate was unaffected by HCN1 gene deletion. These data advance HCN1 channels as a novel molecular target for ketamine, provide a plausible neuronal mechanism for enhanced cortical synchronization during anesthetic-induced hypnosis and suggest that HCN1 channels might contribute to other unexplained actions of ketamine.
authors.affiliation: Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Xiangdong
authors.initials: X
authors.lastname: Chen
authors.forename: Shaofang
authors.initials: S
authors.lastname: Shu
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Bayliss
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D055592:Biophysical Phenomena; D002461:Cell Line, Transformed; D002540:Cerebral Cortex / Q000166:cytology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004558:Electric Stimulation / Q000379:methods; D005045:Etomidate / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D005260:Female; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D066298:In Vitro Techniques; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009433:Neural Inhibition / Q000187:drug effects / Q000235:genetics; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D014162:Transfection
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; C578665:HCN1 protein, human; C578666:Hcn1 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D006993:Hypnotics and Sedatives; D015221:Potassium Channels; D021122:Protein Subunits; D011743:Pyrimidines; C082246:ICI D2788; D049452:Green Fluorescent Proteins; D007649:Ketamine; D005045:Etomidate