scholarly journals All four subunits of HCN2 channels contribute to the activation gating in an additive but intricate manner

2018 ◽  
Vol 150 (9) ◽  
pp. 1261-1271 ◽  
Author(s):  
Mallikarjuna Rao Sunkara ◽  
Tina Schwabe ◽  
Gunter Ehrlich ◽  
Jana Kusch ◽  
Klaus Benndorf
Keyword(s):  
Cyclic Nucleotide ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Activation Mechanism ◽  
Hcn Channels ◽  
Binding Domains ◽  
Activation Gating ◽  
In Trans ◽  
In Cis ◽  
Special Case

Hyperpolarization-activated cyclic nucleotide–modulated (HCN) channels are tetramers that elicit electrical rhythmicity in specialized brain neurons and cardiomyocytes. The channels are dually activated by voltage and binding of cyclic adenosine monophosphate (cAMP) to their four cyclic nucleotide-binding domains (CNBDs). Here we analyze the effects of cAMP binding to different concatemers of HCN2 channel subunits, each having a defined number of functional CNBDs. We show that each liganded CNBD promotes channel activation in an additive manner and that, in the special case of two functional CNBDs, functionality does not depend on the arrangement of the subunits. Correspondingly, the reverse process of deactivation is slowed by progressive liganding, but only if four and three ligands as well as two ligands in trans position (opposite to each other) are bound. In contrast, two ligands bound in cis positions (adjacent to each other) and a single bound ligand do not affect channel deactivation. These results support an activation mechanism in which each single liganded CNBD causes a turning momentum on the tetrameric ring-like structure formed by all four CNBDs and that at least two liganded subunits in trans positions are required to maintain activation.

Ivabradine augments high-frequency dynamic gain of the heart rate response to low- and moderate-intensity vagal nerve stimulation under beta-blockade

2021 ◽  
Author(s):  
Toru Kawada ◽  
Hiromi Yamamoto ◽  
Kazunori Uemura ◽  
Yohsuke Hayama ◽  
Takuya Nishikawa ◽  
...  
Keyword(s):  
Heart Rate ◽  
Nerve Stimulation ◽  
High Frequency ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Vagal Nerve ◽  
Vagal Nerve Stimulation ◽  
Moderate Intensity ◽  
Beta Blockade ◽  
Hcn Channels

Our previous study indicated that intravenously administered ivabradine (IVA) augmented the dynamic heart rate (HR) response to moderate-intensity vagal nerve stimulation (VNS). Considering an accentuated antagonism, the results were somewhat paradoxical; i.e., the accentuated antagonism indicates that an activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels via the accumulation of intracellular cyclic adenosine monophosphate (cAMP) augments the HR response to VNS, whereas the inhibition of HCN channels by IVA also augmented the HR response to VNS. To remove the possible influence from the accentuated antagonism, we examined the effects of IVA on the dynamic vagal control of HR under beta-blockade. In anesthetized rats (n = 7), the right vagal nerve was stimulated for 10 min according to binary white noise signals between 0 and 10 Hz (V0-10), between 0 and 20 Hz (V0-20), and between 0 and 40 Hz (V0-40). The transfer function from VNS to HR was estimated. Under beta-blockade (propranolol, 2 mg/kg, i.v.), IVA (2 mg/kg, i.v.) did not augment the asymptotic low-frequency gain but increased the asymptotic high-frequency gain in V0-10 (0.53 ± 0.10 vs. 1.74 ± 0.40 beats·min−1·Hz−1, P < 0.01) and V0-20 (0.79 ± 0.14 vs. 2.06 ± 0.47 beats·min−1·Hz−1, P < 0.001). These changes, which were observed under a minimal influence from sympathetic background tone, may reflect an increased contribution of the acetylcholine-sensitive potassium channel (IK,ACh) pathway after IVA, because the HR control via the IK,ACh pathway is faster and acts in the frequency range higher than the cAMP-mediated pathway.

scholarly journals HCN channel-mediated neuromodulation can control action potential velocity and fidelity in central axons

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Niklas Byczkowicz ◽  
Abdelmoneim Eshra ◽  
Jacqueline Montanaro ◽  
Andrea Trevisiol ◽  
Johannes Hirrlinger ◽  
...  
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Mossy Fiber ◽  
Mossy Fibers ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Resting Membrane Potential ◽  
Immunogold Electron Microscopy ◽  
Hcn Channels ◽  
Hcn Channel

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels control electrical rhythmicity and excitability in the heart and brain, but the function of HCN channels at the subcellular level in axons remains poorly understood. Here, we show that the action potential conduction velocity in both myelinated and unmyelinated central axons can be bidirectionally modulated by a HCN channel blocker, cyclic adenosine monophosphate (cAMP), and neuromodulators. Recordings from mouse cerebellar mossy fiber boutons show that HCN channels ensure reliable high-frequency firing and are strongly modulated by cAMP (EC50 40 µM; estimated endogenous cAMP concentration 13 µM). In addition, immunogold-electron microscopy revealed HCN2 as the dominating subunit in cerebellar mossy fibers. Computational modeling indicated that HCN2 channels control conduction velocity primarily by altering the resting membrane potential and are associated with significant metabolic costs. These results suggest that the cAMP-HCN pathway provides neuromodulators with an opportunity to finely tune energy consumption and temporal delays across axons in the brain.

Cyclic Nucleotide-Activated Currents in Cultured Olfactory Receptor Neurons of the Hawkmoth Manduca sexta

2008 ◽  
Vol 100 (5) ◽  
pp. 2866-2877 ◽  
Author(s):  
Steffi Krannich ◽  
Monika Stengl
Keyword(s):  
Manduca Sexta ◽  
Cyclic Nucleotide ◽  
Olfactory Receptor ◽  
Low Voltage ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Guanosine Monophosphate ◽  
Olfactory Receptor Neurons ◽  
Cation Channels ◽  
Receptor Neurons

Moth pheromones cause rises in intracellular Ca2+ concentrations that activate Ca2+-dependent cation channels in antennal olfactory receptor neurons. In addition, mechanisms of adaptation and sensitization depend on changes in cyclic nucleotide concentrations. Here, cyclic nucleotide-activated currents in cultured olfactory receptor neurons of the moth Manduca sexta are described, which share properties with currents through vertebrate cyclic nucleotide-gated channels. The cyclic nucleotide-activated currents of M. sexta carried Ca2+ and monovalent cations. They were directly activated by cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), modulated by Ca2+/calmodulin, and inhibited by lanthanum. M. sexta cyclic nucleotide-activated currents developed in an all-or-none manner, which suggests that the underlying channels are coupled and act coordinately. At least one cAMP- and two cGMP-activated nonselective cation currents could be distinguished. Compared with the cAMP-activated current, both cGMP-activated currents appeared to conduct more Ca2+ and showed a stronger down-regulation by Ca2+/calmodulin-dependent negative feedback. Furthermore, both cGMP-activated currents differed in their Ca2+-dependent inhibition. Thus M. sexta olfactory receptor neurons, like vertebrate sensory neurons, appear to express nonselective cyclic nucleotide-activated cation channels with different subunit compositions. Besides the nonselective cyclic nucleotide-activated cation currents, olfactory receptor neurons express a cAMP-dependent current. This current resembled a protein kinase-modulated low-voltage–activated Ca2+ current.

scholarly journals A Cell-Based PDE4 Assay in 1536-Well Plate Format for High-Throughput Screening

2008 ◽  
Vol 13 (7) ◽  
pp. 609-618 ◽  
Author(s):  
Steven A. Titus ◽  
Xiao Li ◽  
Noel Southall ◽  
Jianming Lu ◽  
James Inglese ◽  
...  
Keyword(s):  
Cyclic Nucleotides ◽  
Cyclic Nucleotide ◽  
High Throughput Screening ◽  
Drug Targets ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Cyclic Guanosine Monophosphate ◽  
Guanosine Monophosphate ◽  
Compound Screening ◽  
A Cell

The cyclic nucleotide phosphodiesterases (PDEs) are intracellular enzymes that catalyze the hydrolysis of 3,′5′-cyclic nucleotides, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), to their corresponding 5′nucleotide monophosphates. These enzymes play an important role in controlling cellular concentrations of cyclic nucleotides and thus regulate a variety of cellular signaling events. PDEs are emerging as drug targets for several diseases, including asthma, cardiovascular disease, attention-deficit hyperactivity disorder, Parkinson's disease, and Alzheimer's disease. Although biochemical assays with purified recombinant PDE enzymes and cAMP or cGMP substrate are commonly used for compound screening, cell-based assays would provide a better assessment of compound activity in a more physiological context. The authors report the development and validation of a new cell-based PDE4 assay using a constitutively active G-protein—coupled receptor as a driving force for cAMP production and a cyclic nucleotide—gated cation channel as a biosensor in 1536-well plates. ( Journal of Biomolecular Screening 2008:609-618)

scholarly journals Proposed model of the Dictyostelium cAMP receptors bound to cAMP

2019 ◽  
Author(s):  
Jack Calum Greenhalgh ◽  
Aneesh Chandran ◽  
Matthew Thomas Harper ◽  
Graham Ladds ◽  
Taufiq Rahman
Keyword(s):  
Homology Modelling ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Structural Features ◽  
Activation Mechanism ◽  
Ligand Docking ◽  
Structural Basis ◽  
Intracellular Camp ◽  
Cellular Processes ◽  
Developmental Signalling

Abstract3’,5’-cyclic adenosine monophosphate (cAMP) is well known as a ubiquitous intracellular messenger regulating a diverse array of cellular processes. However, for a group of social amoebae or Dictyostelia undergoing starvation, intracellular cAMP is secreted in a pulsatile manner to their exterior. This then uniquely acts as a first messenger, triggering aggregation of the starving amoebae followed by their developmental progression towards multicellular fruiting bodies formation. Such developmental signalling for extracellularly-acting cAMP is well studied in the popular dictyostelid,Dictyostelium discoideum, and is mediated by a distinct family (‘class E’) of G protein-coupled receptors (GPCRs) collectively designated as the cAMP receptors (cARs). Whilst the biochemical aspects of these receptors are well characterised, little is known about their overall 3D architecture and structural basis for cAMP recognition and subtype-dependent changes in binding affinity. Using a ligand docking-guided homology modelling approach, we hereby present for the first time, plausible models of active forms of the cARs fromD. discoideum. Our models highlight some structural features that may underlie the differential affinities of cAR isoforms for cAMP binding and also suggest few residues that may play important roles for the activation mechanism of this GPCR family.

Sign in / Sign up

Export Citation Format

Share Document