HCN Channels and Cardiac Pacemaking

Singlet oxygen (1O2), which is generated through metabolic reactions and oxidizes numerous biological molecules, has been a useful tool in basic research and clinical practice. However, its role as a signaling factor, as well as a mechanistic understanding of the oxidation process, remains poorly understood. Here, we show that hyperpolarization-activated, cAMP-gated (HCN) channels–which conduct the hyperpolarization-activated current (Ih) and the voltage-insensitive instantaneous current (Iinst), and contribute to diverse physiological functions including learning and memory, cardiac pacemaking, and the sensation of pain–are subject to modification by 1O2. To increase the site specificity of 1O2 generation, we used fluorescein-conjugated cAMP, which specifically binds to HCN channels, or a chimeric channel in which an in-frame 1O2 generator (SOG) protein was fused to the HCN C terminus. Millisecond laser pulses reduced Ih current amplitude, slowed channel deactivation, and enhanced Iinst current. The modification of HCN channel function is a photodynamic process that involves 1O2, as supported by the dependence on dissolved oxygen in solutions, the inhibitory effect by a 1O2 scavenger, and the results with the HCN2-SOG fusion protein. Intriguingly, 1O2 modification of the HCN2 channel is state dependent: laser pulses applied to open channels mainly slow down deactivation and increase Iinst, whereas for the closed channels, 1O2 modification mainly reduced Ih amplitude. We identified a histidine residue (H434 in S6) near the activation gate in the pore critical for 1O2 modulation of HCN function. Alanine replacement of H434 abolished the delay in channel deactivation and the generation of Iinst induced by photodynamic modification. Our study provides new insights into the instantaneous current conducted by HCN channels, showing that modifications to the region close to the intracellular gate underlie the expression of Iinst, and establishes a well-defined model for studying 1O2 modifications at the molecular level.

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f/HCN channels: from a tiny current controlling cardiac pacemaking to a pleiotropic current all over the body.

Progress in Biophysics and Molecular Biology ◽

10.1016/j.pbiomolbio.2021.10.001 ◽

2021 ◽

Author(s):

Annalisa Bucchia ◽

Mirko Baruscottia ◽

Andrea Barbutia

Keyword(s):

The Body ◽

Hcn Channels ◽

Cardiac Pacemaking

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Functional role of HCN channels within a looming sensitive neuron for visually evoked escape

Frontiers in Behavioral Neuroscience ◽

10.3389/conf.fnbeh.2012.27.00170 ◽

2012 ◽

Vol 6 ◽

Author(s):

Gabbiani Fabrizio

Keyword(s):

Functional Role ◽

Hcn Channels

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Faculty Opinions recommendation of HCN channels segregate stimulation-evoked movement responses in neocortex and allow for coordinated forelimb movements in rodents.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.726694431.793530281 ◽

2017 ◽

Author(s):

Andrew Jackson ◽

Wei Xu

Keyword(s):

Hcn Channels ◽

Forelimb Movements

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Pharmacology of Ivabradine and the Effect on Chronic Heart Failure

Current Topics in Medicinal Chemistry ◽

10.2174/1568026619666190809093144 ◽

2019 ◽

Vol 19 (21) ◽

pp. 1878-1901 ◽

Cited By ~ 3

Author(s):

Yue Zhou ◽

Jian Wang ◽

Zhuo Meng ◽

Shuang Zhou ◽

Jiayu Peng ◽

...

Keyword(s):

Heart Failure ◽

Heart Rate ◽

Chronic Heart Failure ◽

Underlying Mechanism ◽

Clinical Syndrome ◽

Hcn Channels ◽

Therapeutic Effects ◽

Diastolic Depolarization ◽

High Incidence ◽

Spontaneous Phase

Chronic Heart Failure (CHF) is a complex clinical syndrome with a high incidence worldwide. Although various types of pharmacological and device therapies are available for CHF, the prognosis is not ideal, for which, the control of increased Heart Rate (HR) is critical. Recently, a bradycardic agent, ivabradine, is found to reduce HR by inhibiting the funny current (If). The underlying mechanism states that ivabradine can enter the Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels and bind to the intracellular side, subsequently inhibiting the If. This phenomenon can prolong the slow spontaneous phase in the diastolic depolarization, and thus, reduce HR. The clinical trials demonstrated the significant effects of the drug on reducing HR and improving the symptoms of CHF with fewer adverse effects. This review primarily introduces the chemical features and pharmacological characteristics of ivabradine and the mechanism of treating CHF. Also, some expected therapeutic effects on different diseases were also concluded. However, ivabradine, as a typical If channel inhibitor, necessitates additional research to verify its pharmacological functions.

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Assembly of the Cardiac Pacemaking Complex: Electrogenic Principles of Sinoatrial Node Morphogenesis

Journal of Cardiovascular Development and Disease ◽

10.3390/jcdd8040040 ◽

2021 ◽

Vol 8 (4) ◽

pp. 40

Author(s):

Marietta Easterling ◽

Simone Rossi ◽

Anthony J Mazzella ◽

Michael Bressan

Keyword(s):

Cardiac Tissue ◽

Sinoatrial Node ◽

Cardiac Pacemaker ◽

Tissue Level ◽

Rhythmic Contraction ◽

Entire Volume ◽

Impulse Generation ◽

Cardiac Pacemaking ◽

Electrical Impulses ◽

Sufficient Strength

Cardiac pacemaker cells located in the sinoatrial node initiate the electrical impulses that drive rhythmic contraction of the heart. The sinoatrial node accounts for only a small proportion of the total mass of the heart yet must produce a stimulus of sufficient strength to stimulate the entire volume of downstream cardiac tissue. This requires balancing a delicate set of electrical interactions both within the sinoatrial node and with the downstream working myocardium. Understanding the fundamental features of these interactions is critical for defining vulnerabilities that arise in human arrhythmic disease and may provide insight towards the design and implementation of the next generation of potential cellular-based cardiac therapeutics. Here, we discuss physiological conditions that influence electrical impulse generation and propagation in the sinoatrial node and describe developmental events that construct the tissue-level architecture that appears necessary for sinoatrial node function.

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AAV-Mediated CRISPRi and RNAi Based Gene Silencing in Mouse Hippocampal Neurons

Cells ◽

10.3390/cells10020324 ◽

2021 ◽

Vol 10 (2) ◽

pp. 324

Author(s):

Matthias Deutsch ◽

Anne Günther ◽

Rodrigo Lerchundi ◽

Christine R. Rose ◽

Sabine Balfanz ◽

...

Keyword(s):

Gene Expression ◽

Transcription Initiation ◽

Hippocampal Neurons ◽

De Novo ◽

Protein Biosynthesis ◽

Physiological Role ◽

High Specificity ◽

Hcn Channels ◽

Proliferating Cells ◽

Neuronal Tissues

Uncovering the physiological role of individual proteins that are part of the intricate process of cellular signaling is often a complex and challenging task. A straightforward strategy of studying a protein’s function is by manipulating the expression rate of its gene. In recent years, the Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/Cas9-based technology was established as a powerful gene-editing tool for generating sequence specific changes in proliferating cells. However, obtaining homogeneous populations of transgenic post-mitotic neurons by CRISPR/Cas9 turned out to be challenging. These constraints can be partially overcome by CRISPR interference (CRISPRi), which mediates the inhibition of gene expression by competing with the transcription machinery for promoter binding and, thus, transcription initiation. Notably, CRISPR/Cas is only one of several described approaches for the manipulation of gene expression. Here, we targeted neurons with recombinant Adeno-associated viruses to induce either CRISPRi or RNA interference (RNAi), a well-established method for impairing de novo protein biosynthesis by using cellular regulatory mechanisms that induce the degradation of pre-existing mRNA. We specifically targeted hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels, which are widely expressed in neuronal tissues and play essential physiological roles in maintaining biophysical characteristics in neurons. Both of the strategies reduced the expression levels of three HCN isoforms (HCN1, 2, and 4) with high specificity. Furthermore, detailed analysis revealed that the knock-down of just a single HCN isoform (HCN4) in hippocampal neurons did not affect basic electrical parameters of transduced neurons, whereas substantial changes emerged in HCN-current specific properties.

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