Journal article
Bidirectional flow of the funny current (If) during the pacemaking cycle in murine sinoatrial node myocytes
Proceedings of the National Academy of Sciences of the United States of America, Vol.118(28), e2104668118
07/01/2021
DOI: 10.1073/pnas.2104668118
PMCID: PMC8285948
PMID: 34260402
Abstract
Sinoatrial node myocytes (SAMs) act as cardiac pacemaker cells by firing spontaneous action potentials (APs) that initiate each heartbeat. The funny current (If) is critical for the generation of these spontaneous APs; however, its precise role during the pacemaking cycle remains unresolved. Here, we used the AP-clamp technique to quantify If during the cardiac cycle in mouse SAMs. We found that If is persistently active throughout the sinoatrial AP, with surprisingly little voltage-dependent gating. As a consequence, it carries both inward and outward current around its reversal potential of -30 mV. Despite operating at only 2 to 5% of its maximal conductance, If carries a substantial fraction of both depolarizing and repolarizing net charge movement during the firing cycle. We also show that β-adrenergic receptor stimulation increases the percentage of net depolarizing charge moved by If, consistent with a contribution of If to the fight-or-flight increase in heart rate. These properties were confirmed by heterologously expressed HCN4 channels and by mathematical models of If Modeling further suggested that the slow rates of activation and deactivation of the HCN4 isoform underlie the persistent activity of If during the sinoatrial AP. These results establish a new conceptual framework for the role of If in pacemaking, in which it operates at a very small fraction of maximal activation but nevertheless drives membrane potential oscillations in SAMs by providing substantial driving force in both inward and outward directions.
Details
- Title: Subtitle
- Bidirectional flow of the funny current (If) during the pacemaking cycle in murine sinoatrial node myocytes
- Creators
- Colin H PetersPin W LiuStefano MorottiStephanie C GantzEleonora GrandiBruce P BeanCatherine Proenza
- Resource Type
- Journal article
- Publication Details
- Proceedings of the National Academy of Sciences of the United States of America, Vol.118(28), e2104668118
- DOI
- 10.1073/pnas.2104668118
- PMID
- 34260402
- PMCID
- PMC8285948
- ISSN
- 0027-8424
- eISSN
- 1091-6490
- Grant note
- DOI: 10.13039/100000050, name: HHS | NIH | National Heart, Lung, and Blood Institute, award: HL 088427; DOI: 10.13039/100000065, name: HHS | NIH | National Institute of Neurological Disorders and Stroke, award: NS 036855; DOI: 10.13039/100000050, name: HHS | NIH | National Heart, Lung, and Blood Institute, award: HL 131517; DOI: 10.13039/100000050, name: HHS | NIH | National Heart, Lung, and Blood Institute, award: HL 141214; DOI: 10.13039/100000050, name: HHS | NIH | National Heart, Lung, and Blood Institute, award: 141084; DOI: 10.13039/100000002, name: HHS | National Institutes of Health, award: OT2OD026580; DOI: 10.13039/100000050, name: HHS | NIH | National Heart, Lung, and Blood Institute, award: HL 138160; DOI: 10.13039/100000968, name: American Heart Association, award: 19POST34380777
- Language
- English
- Date published
- 07/01/2021
- Academic Unit
- Molecular Physiology and Biophysics; Iowa Neuroscience Institute
- Record Identifier
- 9984442029302771
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