Activation gating in HCN2 channels

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels control electrical rhythmicity in specialized brain and heart cells. We quantitatively analysed voltage-dependent activation of homotetrameric HCN2 channels and its modulation by the second messenger cAMP using global fits of hidden Markovian models to complex experimental data. We show that voltage-dependent activation is essentially governed by two separable voltage-dependent steps followed by voltage-independent opening of the pore. According to this model analysis, the binding of cAMP to the channels exerts multiple effects on the voltage-dependent gating: It stabilizes the open pore, reduces the total gating charge from ~8 to ~5, makes an additional closed state outside the activation pathway accessible and strongly accelerates the ON-gating but not the OFF-gating. Furthermore, the open channel has a much slower computed OFF-gating current than the closed channel, in both the absence and presence of cAMP. Together, these results provide detailed new insight into the voltage- and cAMP-induced activation gating of HCN channels.

[1]  J. Tytgat,et al.  Functional Heteromerization of HCN1 and HCN2 Pacemaker Channels* , 2001, The Journal of Biological Chemistry.

[2]  R. Shigemoto,et al.  Immunohistochemical localization of Ih channel subunits, HCN1–4, in the rat brain , 2004, The Journal of comparative neurology.

[3]  B. Santoro,et al.  The HCN Gene Family: Molecular Basis of the Hyperpolarization‐Activated Pacemaker Channels , 1999, Annals of the New York Academy of Sciences.

[4]  W. Catterall,et al.  Overview of Molecular Relationships in the Voltage-Gated Ion Channel Superfamily , 2005, Pharmacological Reviews.

[5]  K. Benndorf,et al.  Conformational Flip of Nonactivated HCN2 Channel Subunits Evoked by Cyclic Nucleotides , 2015, Biophysical journal.

[6]  S. Siegelbaum,et al.  Voltage Sensor Movement and cAMP Binding Allosterically Regulate an Inherently Voltage-independent Closed−Open Transition in HCN Channels , 2007, The Journal of general physiology.

[7]  T. Ishii,et al.  Determinants of activation kinetics in mammalian hyperpolarization‐activated cation channels , 2001, The Journal of physiology.

[8]  Baron Chanda,et al.  Free-energy relationships in ion channels activated by voltage and ligand , 2013, The Journal of general physiology.

[9]  E. C. Young,et al.  Cytoplasmic cAMP-sensing domain of hyperpolarization-activated cation (HCN) channels uses two structurally distinct mechanisms to regulate voltage gating , 2010, Proceedings of the National Academy of Sciences.

[10]  S. Siegelbaum,et al.  Properties of Hyperpolarization-Activated Pacemaker Current Defined by Coassembly of Hcn1 and Hcn2 Subunits and Basal Modulation by Cyclic Nucleotide , 2001, The Journal of general physiology.

[11]  W. N. Zagotta,et al.  CNG and HCN channels: two peas, one pod. , 2006, Annual review of physiology.

[12]  M. Biel,et al.  Dominant-Negative Suppression of HCN Channels Markedly Reduces the Native Pacemaker Current If and Undermines Spontaneous Beating of Neonatal Cardiomyocytes , 2003, Circulation.

[13]  A. Hodgkin,et al.  A quantitative description of membrane current and its application to conduction and excitation in nerve , 1952, The Journal of physiology.

[14]  D. DiFrancesco,et al.  Heteromeric HCN1–HCN4 Channels: A Comparison with Native Pacemaker Channels from the Rabbit Sinoatrial Node , 2003, The Journal of physiology.

[15]  C. Wahl-Schott,et al.  Hyperpolarization-activated cation channels: from genes to function. , 2009, Physiological reviews.

[16]  F. Saitow,et al.  Excitability increase induced by beta-adrenergic receptor-mediated activation of hyperpolarization-activated cation channels in rat cerebellar basket cells. , 2000, Journal of neurophysiology.

[17]  Martin Biel,et al.  Two pacemaker channels from human heart with profoundly different activation kinetics , 1999, The EMBO journal.

[18]  R. Aldrich,et al.  Allosteric Voltage Gating of Potassium Channels I: Mslo Ionic Currents in the Absence of Ca2+ , 1999 .

[19]  Rich Olson,et al.  Structural basis for modulation and agonist specificity of HCN pacemaker channels , 2003, Nature.

[20]  S. Siegelbaum,et al.  Regulation of Hyperpolarization-Activated Hcn Channel Gating and Camp Modulation Due to Interactions of Cooh Terminus and Core Transmembrane Regions , 2001, The Journal of general physiology.

[21]  Dario DiFrancesco,et al.  Integrated Allosteric Model of Voltage Gating of Hcn Channels , 2001, The Journal of general physiology.

[22]  F. Elinder,et al.  Mode shifts in the voltage gating of the mouse and human HCN2 and HCN4 channels , 2006, The Journal of physiology.

[23]  Adrian Y. C. Wong,et al.  Modulation of a presynaptic hyperpolarization‐activated cationic current (Ih) at an excitatory synaptic terminal in the rat auditory brainstem , 2001, The Journal of physiology.

[24]  U. Kaupp,et al.  Molecular identification of a hyperpolarization-activated channel in sea urchin sperm , 1998, Nature.

[25]  F. Elinder,et al.  Hysteresis in the Voltage Dependence of HCN Channels , 2005, The Journal of general physiology.

[26]  M. Biel,et al.  A family of hyperpolarization-activated mammalian cation channels , 1998, Nature.

[27]  D DiFrancesco,et al.  Dual allosteric modulation of pacemaker (f) channels by cAMP and voltage in rabbit SA node , 1999, The Journal of physiology.

[28]  Klaus Benndorf,et al.  Probability Fluxes and Transition Paths in a Markovian Model Describing Complex Subunit Cooperativity in HCN2 Channels , 2012, PLoS Comput. Biol..

[29]  K. Benndorf,et al.  Elementary functional properties of single HCN2 channels. , 2013, Biophysical journal.

[30]  Zhanna V. Vysotskaya,et al.  Structural Basis for the cAMP-dependent Gating in the Human HCN4 Channel* , 2010, The Journal of Biological Chemistry.

[31]  U. Kaupp,et al.  Molecular diversity of pacemaker ion channels. , 2001, Annual review of physiology.

[32]  Klaus Benndorf,et al.  How subunits cooperate in cAMP-induced activation of homotetrameric HCN2 channels. , 2012, Nature chemical biology.

[33]  J. Williams,et al.  Modulation of the hyperpolarization‐activated current (Ih) by cyclic nucleotides in guinea‐pig primary afferent neurons. , 1996, The Journal of physiology.

[34]  S. Heinemann,et al.  A characterization of the activating structural rearrangements in voltage-dependent Shaker K+ channels , 1994, Neuron.

[35]  R. Pearce,et al.  Hyperpolarization-activated cation current (Ih) in neurons of the medial nucleus of the trapezoid body: voltage-clamp analysis and enhancement by norepinephrine and cAMP suggest a modulatory mechanism in the auditory brain stem. , 1993, Journal of neurophysiology.

[36]  D James Surmeier,et al.  HCN2 and HCN1 Channels Govern the Regularity of Autonomous Pacemaking and Synaptic Resetting in Globus Pallidus Neurons , 2004, The Journal of Neuroscience.

[37]  Eric R Kandel,et al.  Identification of a Gene Encoding a Hyperpolarization-Activated Pacemaker Channel of Brain , 1998, Cell.

[38]  A. Bruening-Wright,et al.  Kinetic Relationship between the Voltage Sensor and the Activation Gate in spHCN Channels , 2007, The Journal of general physiology.

[39]  S. Siegelbaum,et al.  Hyperpolarization-activated cation currents: from molecules to physiological function. , 2003, Annual review of physiology.

[40]  M. Biel,et al.  Cellular expression and functional characterization of four hyperpolarization-activated pacemaker channels in cardiac and neuronal tissues. , 2001, European journal of biochemistry.

[41]  H. Brown,et al.  How does adrenaline accelerate the heart? , 1979, Nature.

[42]  Reinhard Seifert,et al.  PACEMAKER OSCILLATIONS IN HEART AND BRAIN: A KEY ROLE FOR HYPERPOLARIZATION-ACTIVATED CATION CHANNELS , 2000, Chronobiology international.

[43]  Dario DiFrancesco,et al.  Characterization of single pacemaker channels in cardiac sino-atrial node cells , 1986, Nature.

[44]  D. Colquhoun,et al.  Binding, gating, affinity and efficacy: The interpretation of structure‐activity relationships for agonists and of the effects of mutating receptors , 1998, British journal of pharmacology.

[45]  T. Zimmer,et al.  Interdependence of Receptor Activation and Ligand Binding in HCN2 Pacemaker Channels , 2010, Neuron.

[46]  M. Nardini,et al.  Tetramerization Dynamics of C-terminal Domain Underlies Isoform-specific cAMP Gating in Hyperpolarization-activated Cyclic Nucleotide-gated Channels* , 2011, The Journal of Biological Chemistry.

[47]  S. Siegelbaum,et al.  Molecular and Functional Heterogeneity of Hyperpolarization-Activated Pacemaker Channels in the Mouse CNS , 2000, The Journal of Neuroscience.

[48]  S. Siegelbaum,et al.  Constraining Ligand-Binding Site Stoichiometry Suggests that a Cyclic Nucleotide–Gated Channel Is Composed of Two Functional Dimers , 1998, Neuron.

[49]  Huxley Af,et al.  A quantitative description of membrane current and its application to conduction and excitation in nerve. 1952. , 1990 .

[50]  Matthew F Nolan,et al.  Activity-Dependent Regulation of HCN Pacemaker Channels by Cyclic AMP Signaling through Dynamic Allosteric Coupling , 2002, Neuron.

[51]  J. Changeux,et al.  ON THE NATURE OF ALLOSTERIC TRANSITIONS: A PLAUSIBLE MODEL. , 1965, Journal of molecular biology.

[52]  Unraveling subunit cooperativity in homotetrameric HCN2 channels. , 2012, Biophysical journal.

[53]  R. MacKinnon,et al.  Structures of the Human HCN1 Hyperpolarization-Activated Channel , 2017, Cell.

[54]  S. Jones,et al.  Calcium currents in the A7r5 smooth muscle-derived cell line. An allosteric model for calcium channel activation and dihydropyridine agonist action , 1992, The Journal of general physiology.

[55]  F. Hofmann,et al.  Functional Expression of the Human HCN3 Channel* , 2005, Journal of Biological Chemistry.

[56]  M. Mazzanti,et al.  Properties of the hyperpolarizing‐activated current (if) in cells isolated from the rabbit sino‐atrial node. , 1986, The Journal of physiology.

[57]  K. Benndorf,et al.  Relating ligand binding to activation gating in CNGA2 channels , 2007, Nature.