title: Cell-specific Dynamic Clamp analysis of the role of funny If current in cardiac pacemaking.
abstract: We used the Dynamic Clamp technique for i) comparative validation of conflicting computational models of the hyperpolarization-activated funny current, If, and ii) quantification of the role of If in mediating autonomic modulation of heart rate. Experimental protocols based on the injection of a real-time recalculated synthetic If current in sinoatrial rabbit cells were developed. Preliminary results of experiments mimicking the autonomic modulation of If demonstrated the need for a customization procedure to compensate for cellular heterogeneity. For this reason, we used a cell-specific approach, scaling the maximal conductance of the injected current based on the cell's spontaneous firing rate. The pacemaking rate, which was significantly reduced after application of Ivabradine, was restored by the injection of synthetic current based on the Severi-DiFrancesco formulation, while the injection of synthetic current based on the Maltsev-Lakatta formulation did not produce any significant variation. A positive virtual shift of the If activation curve, mimicking the Isoprenaline effects, led to a significant increase in pacemaking rate (+17.3 ± 6.7%, p < 0.01), although of lower magnitude than that induced by real Isoprenaline (+45.0 ± 26.1%). Similarly, a negative virtual shift of the activation curve significantly lowered the pacemaking rate (-11.8 ± 1.9%, p < 0.001), as did the application of real Acetylcholine (-20.5 ± 5.1%). The Dynamic Clamp approach, applied to the If study in cardiomyocytes for the first time and rate-adapted to manage intercellular variability, indicated that: i) the quantitative description of the If current in the Severi-DiFrancesco model accurately reproduces the effects of the real current on rabbit sinoatrial cell pacemaking rate and ii) a significant portion (50-60%) of the physiological autonomic rate modulation is due to the shift of the If activation curve.
authors.affiliation: Computational Physiopathology Unit, Laboratory of Cellular and Molecular Engineering, D.E.I., University of Bologna, Via Venezia 52, 47521 Cesena, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Ravagli
authors.affiliation: The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Bucchi
authors.affiliation: Computational Physiopathology Unit, Laboratory of Cellular and Molecular Engineering, D.E.I., University of Bologna, Via Venezia 52, 47521 Cesena, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Bartolucci
authors.affiliation: The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Paina
authors.affiliation: The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Baruscotti
authors.affiliation: The PaceLab, Department of Biosciences, University of Milan, Via Celoria 26, 20133 Milano, Italy.
authors.forename: D
authors.initials: D
authors.lastname: DiFrancesco
authors.affiliation: Computational Physiopathology Unit, Laboratory of Cellular and Molecular Engineering, D.E.I., University of Bologna, Via Venezia 52, 47521 Cesena, Italy. Electronic address: stefano.severi@unibo.it.
authors.forename: S
authors.initials: S
authors.lastname: Severi
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D003584:Cytological Techniques; D055724:Electrophysiological Phenomena / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000378:metabolism*; D000077550:Ivabradine; D008955:Models, Cardiovascular; D011817:Rabbits; D059010:Single-Cell Analysis; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
chemical_list: D001552:Benzazepines; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D000077550:Ivabradine; D000109:Acetylcholine
keywords: Autonomic modulation; Cardiac pacemaking; Computational modeling; Dynamic Clamp; Funny current; Sinoatrial node