title: Impact of detubulation on force and kinetics of cardiac muscle contraction.
abstract: Action potential-driven Ca(2+) currents from the transverse tubules (t-tubules) trigger synchronous Ca(2+) release from the sarcoplasmic reticulum of cardiomyocytes. Loss of t-tubules has been reported in cardiac diseases, including heart failure, but the effect of uncoupling t-tubules from the sarcolemma on cardiac muscle mechanics remains largely unknown. We dissected intact rat right ventricular trabeculae and compared force, sarcomere length, and intracellular Ca(2+) in control trabeculae with trabeculae in which the t-tubules were uncoupled from the plasma membrane by formamide-induced osmotic shock (detubulation). We verified disconnection of a consistent fraction of t-tubules from the sarcolemma by two-photon fluorescence imaging of FM4-64-labeled membranes and by the absence of tubular action potential, which was recorded by random access multiphoton microscopy in combination with a voltage-sensitive dye (Di-4-AN(F)EPPTEA). Detubulation reduced the amplitude and prolonged the duration of Ca(2+) transients, leading to slower kinetics of force generation and relaxation and reduced twitch tension (1 Hz, 30°C, 1.5 mM [Ca(2+)]o). No mechanical changes were observed in rat left atrial trabeculae after formamide shock, consistent with the lack of t-tubules in rodent atrial myocytes. Detubulation diminished the rate-dependent increase of Ca(2+)-transient amplitude and twitch force. However, maximal twitch tension at high [Ca(2+)]o or in post-rest potentiated beats was unaffected, although contraction kinetics were slower. The ryanodine receptor (RyR)2 Ca-sensitizing agent caffeine (200 µM), which increases the velocity of transverse Ca(2+) release propagation in detubulated cardiomyocytes, rescued the depressed contractile force and the slower twitch kinetics of detubulated trabeculae, with negligible effects in controls. We conclude that partial loss of t-tubules leads to myocardial contractile abnormalities that can be rescued by enhancing and accelerating the propagation of Ca(2+)-induced Ca(2+) release to orphan RyR2 clusters.
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy cecilia.ferrantini@unifi.it.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Ferrantini
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Coppini
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy National Institute of Optics, National Research Council, 50019 Sesto Fiorentino, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Sacconi
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Tosi
authors.affiliation: Department of Cardiac Sciences of the Libin Institute at the Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Mei Luo
authors.initials: ML
authors.lastname: Zhang
authors.affiliation: Department of Cardiac Sciences of the Libin Institute at the Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Guo Liang
authors.initials: GL
authors.lastname: Wang
authors.affiliation: Department of Cardiac Sciences of the Libin Institute at the Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Ewout
authors.initials: E
authors.lastname: de Vries
authors.affiliation: Department of Cardiac Sciences of the Libin Institute at the Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Ernst
authors.initials: E
authors.lastname: Hoppenbrouwers
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy National Institute of Optics, National Research Council, 50019 Sesto Fiorentino, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pavone
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Cerbai
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Tesi
authors.affiliation: Center of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, ItalyCenter of Molecular Medicine, Department of Experimental and Clinical Medicine, Division of Physiology, Department of NeuroFarBa, Division of Pharmacology, LENS, European Laboratory for Non-Linear Spectroscopy, and Department of Physics, University of Florence, 50121 Florence, Italy.
authors.forename: Corrado
authors.initials: C
authors.lastname: Poggesi
authors.affiliation: Department of Cardiac Sciences of the Libin Institute at the Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Henk E D J
authors.initials: HE
authors.lastname: ter Keurs
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D056966:Excitation Contraction Coupling / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D007700:Kinetics; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*