Molecular mechanism of cAMP modulation of HCN pacemaker channels

Abstract

Hyperpolarization-activated cation channels of the HCN gene family contribute to spontaneous rhythmic activity in both heart and brain. All four family members contain both a core transmembrane segment domain, homologous to the S1-S6 regions of voltage-gated K+ channels, and a carboxy-terminal 120 amino-acid cyclic nucleotide-binding domain (CNBD) motif. Homologous CNBDs are responsible for the direct activation of cyclic nucleotide-gated channels and for modulation of the HERG voltage-gated K+ channel--important for visual and olfactory signalling and for cardiac repolarization, respectively. The direct binding of cyclic AMP to the cytoplasmic site on HCN channels permits the channels to open more rapidly and completely after repolarization of the action potential, thereby accelerating rhythmogenesis. However, the mechanism by which cAMP binding modulates HCN channel gating and the basis for functional differences between HCN isoforms remain unknown. Here we demonstrate by constructing truncation mutants that the CNBD inhibits activation of the core transmembrane domain. cAMP binding relieves this inhibition. Differences in activation gating and extent of cAMP modulation between the HCN1 and HCN2 isoforms result largely from differences in the efficacy of CNBD inhibition.

PIP2-Mediated HCN3 Channel Gating Is Crucial for Rhythmic Burst Firing in Thalamic Intergeniculate Leaflet Neurons

“…3E), and significantly increased the deactivation time constant. The observed effects on the kinetics are consistent with cAMP-mediated stabilization of a cAMP-sensitive channel (such as HCN2) in the open state (Wainger et al, 2001;Wicks et al, 2011). The pronounced effect of 8-Br cAMP on I h in vLGN neurons is consistent with the immunolabeling data demonstrating high levels of HCN2 immunoreactivity in the vLGN (Notomi and Shigemoto, 2004).…”

“…Data processing including the construction of activation curves, fit of time constants, and measurements of sag, burst and tonic spike firing was performed using MiniAnalysis (Synaptosoft) and Clampfit V.10, as previously described for neurons (Ying and Goldstein, 2005;Ying et al, 2006Ying et al, , 2007b. Data analyses for oocyte recordings were performed using PulseFit (HEKA Elektronik) and IgorPro (Wavemetrics, as previously reported (Santoro et al, 2000;Wainger et al, 2001;Fogle et al, 2007). Single-exponential time constants were obtained by fitting the first 4 s of the neuronal current trace (cf.…”

“…Subcloning and expression of hHCN3 were performed much as previously described (Goulding et al, 1993;Wainger et al, 2001). Thus, PCR amplification was used to introduce an XbaI site and idealized Kozak sequence (TCTAGAGCCGCCACC) immediately 5Ј to the initiating methionine of the ORF of hHCN3 and a HinDIII site immediately 3Ј to the stop codon.…”

Formation of heteromeric hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in the hippocampus is regulated by developmental seizures

“…In hippocampus, these currents contribute to maintenance of resting membrane potential (Lupica et al, 2001), shape rhythmic and synchronized neuronal activity (Maccaferri and McBain, 1996;Magee, 1999) and regulate the temporal summation of dendritic depolarization (Magee, 1998;Poolos et al, 2002). Short-term modulation of HCN channel function is mediated by cAMP, influencing channel kinetics and voltage dependent activation curves (DiFrancesco, 1993;Waigner et al, 2001). Recently, long-term modulation of the properties of I h currents has been suggested to result from regulated changes in channel subunit expression (Bräuer et al, 2001;Brewster et al, 2002;Santoro and Baram, 2003).…”

Structural snapshot of cyclic nucleotide binding domains from cyclic nucleotide-sensitive ion channels

“…Several additional van der Waals interactions are formed by residues R632 of helix αC, and V564, M572 and L574 located in the β roll ( Figure 3A). The interactions of helix αC are of particular interest, because mutations of residues located in αC in HCN and CNG channels impair ligand sensitivity and perturb channel function (Varnum et al, 1995;Matulef et al, 1999;Wainger et al, 2001).…”