title: HCN hyperpolarization-activated cation channels strengthen virtual nicotinic EPSPs and thereby elevate synaptic amplification in rat sympathetic neurons.
abstract: The influence of hyperpolarization-activated cation current (h-current; Ih) upon synaptic integration in paravertebral sympathetic neurons was studied together with expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) subunit isoforms. All four HCN subunits were detected in homogenates of the rat superior cervical ganglion (SCG) using the PCR to amplify reverse-transcribed messenger RNAs (RT-PCR) and using quantitative PCR. Voltage clamp recordings from dissociated SCG neurons at 35°C detected Ih in all cells, with a maximum hyperpolarization-activated cation conductance of 1.2 ± 0.1 nS, half-maximal activation at -87.6 mV, and reversal potential of -31.6 mV. Interaction between Ih and synaptic potentials was tested with virtual fast nicotinic excitatory postsynaptic potentials (EPSPs) created with dynamic clamp. The blocking of Ih with 15 μM ZD7288 hyperpolarized cells by 4.7 mV and increased the virtual synaptic conductance required to stimulate an action potential from 7.0 ± 0.9 nS to 12.1 ± 0.9 nS. In response to stimulation with 40 s long trains of virtual EPSPs, ZD7288 reduced postsynaptic firing from 2.2 to 1.7 Hz and the associated synaptic amplification from 2.2 ± 0.1 to 1.7 ± 0.2. Cyclic nucleotide binding to HCN channels was simulated by blocking native Ih with ZD7288, followed by reconstitution with virtual Ih using a dynamic clamp model of the voltage clamp data. Over a 30-mV range, shifting the half-activation voltage for Ih in 10 mV depolarizing increments always increased synaptic gain. These results indicate that Ih, in sympathetic neurons, can strengthen nicotinic EPSPs and increase synaptic amplification, while also working as a substrate for cyclic nucleotide-dependent modulation.
authors.affiliation: Department of Neurobiology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors.forename: Paul H M
authors.initials: PH
authors.lastname: Kullmann
authors.affiliation: Department of Neurobiology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors.forename: Kristine M
authors.initials: KM
authors.lastname: Sikora
authors.affiliation: Department of Neurobiology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors.forename: K Lyles
authors.initials: KL
authors.lastname: Clark
authors.affiliation: Department of Neurobiology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors.forename: Irene
authors.initials: I
authors.lastname: Arduini
authors.affiliation: Department of Neurobiology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors.forename: Mitchell G
authors.initials: MG
authors.lastname: Springer
authors.affiliation: Department of Neurobiology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania jph@pitt.edu.
authors.forename: John P
authors.identifier: 0000-0001-5516-0210
authors.initials: JP
authors.lastname: Horn
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena / Q000187:drug effects / Q000502:physiology; D001703:Biophysics; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects*; D005260:Female; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000235:genetics / Q000378:metabolism*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009478:Neuropeptide Y / Q000235:genetics / Q000378:metabolism; D009538:Nicotine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017783:Superior Cervical Ganglion / Q000166:cytology*; D013569:Synapses / Q000187:drug effects; D014584:User-Computer Interface
chemical_list: D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D009478:Neuropeptide Y; D011743:Pyrimidines; D012333:RNA, Messenger; C082246:ICI D2788; D009538:Nicotine
keywords: baroreflex gain; blood pressure; dynamic clamp; sympathetic motor system; synaptic integration