Dendritic excitability of mouse frontal cortex pyramidal neurons is shaped by the interaction among HCN, Kir2, and Kleak channels.
Dendritically placed, voltage-sensitive ion channels are key regulators of neuronal synaptic integration. In several cell types, hyperpolarization/cyclic nucleotide gated (HCN) cation channels figure prominently in dendritic mechanisms controlling the temporal summation of excitatory synaptic events. In prefrontal cortex, the sustained activity of pyramidal neurons in working memory tasks is thought to depend on the temporal summation of dendritic excitatory inputs. Yet we know little about how this is accomplished in these neurons and whether HCN channels play a role. To gain a better understanding of this process, layer V-VI pyramidal neurons in slices of mouse prelimbic and infralimbic cortex were studied. Somatic voltage-clamp experiments revealed the presence of rapidly activating and deactivating cationic currents attributable to HCN1/HCN2 channels. These channels were open at the resting membrane potential and had an apparent half-activation voltage near -90 mV. In the same voltage range, K+ currents attributable to Kir2.2/2.3 and K+-selective leak (Kleak) channels were prominent. Computer simulations grounded in the biophysical measurements suggested a dynamic interaction among Kir2, Kleak, and HCN channel currents in shaping membrane potential and the temporal integration of synaptic potentials. This inference was corroborated by experiment. Blockade of Kir2/Kleak channels caused neurons to depolarize, leading to the deactivation of HCN channels, the initiation of regular spiking (4-5 Hz), and enhanced temporal summation of EPSPs. These studies show that HCN channels are key regulators of synaptic integration in prefrontal pyramidal neurons but that their functional contribution is dependent on a partnership with Kir2 and Kleak channels.
Day
Michelle
M
Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
Carr
David B
DB
Ulrich
Sasha
S
Ilijic
Ema
E
Tkatch
Tatiana
T
Surmeier
D James
DJ
D000818:Animals; D002478:Cells, Cultured; D054815:Cyclic Nucleotide-Gated Cation Channels; D003712:Dendrites / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005260:Female; D005625:Frontal Lobe / Q000166:cytology / Q000502:physiology*; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain / Q000502:physiology*; D011247:Pregnancy; D017966:Pyramidal Cells / Q000502:physiology*
D054815:Cyclic Nucleotide-Gated Cation Channels; C578666:Hcn1 protein, mouse; C578711:Hcn2 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; C489463:Kir2.2 channel; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D024683:Potassium Channels, Tandem Pore Domain