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Frisk M, Ruud M, Espe EKS, Aronsen JM, Røe ÅT, Zhang L, Norseng PA, Sejersted OM, Christensen GA, Sjaastad I, Louch WE. Elevated ventricular wall stress disrupts cardiomyocyte t-tubule structure and calcium homeostasis. Cardiovasc Res 2016; 112:443-51. [PMID: 27226008 PMCID: PMC5031949 DOI: 10.1093/cvr/cvw111] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 05/16/2016] [Indexed: 11/13/2022] Open
Abstract
AIMS Invaginations of the cellular membrane called t-tubules are essential for maintaining efficient excitation-contraction coupling in ventricular cardiomyocytes. Disruption of t-tubule structure during heart failure has been linked to dyssynchronous, slowed Ca(2+) release and reduced power of the heartbeat. The underlying mechanism is, however, unknown. We presently investigated whether elevated ventricular wall stress triggers remodelling of t-tubule structure and function. METHODS AND RESULTS MRI and blood pressure measurements were employed to examine regional wall stress across the left ventricle of sham-operated and failing, post-infarction rat hearts. In failing hearts, elevated left ventricular diastolic pressure and ventricular dilation resulted in markedly increased wall stress, particularly in the thin-walled region proximal to the infarct. High wall stress in this proximal zone was associated with reduced expression of the dyadic anchor junctophilin-2 and disrupted cardiomyocyte t-tubular structure. Indeed, local wall stress measurements predicted t-tubule density across sham and failing hearts. Elevated wall stress and disrupted cardiomyocyte structure in the proximal zone were also associated with desynchronized Ca(2+) release in cardiomyocytes and markedly reduced local contractility in vivo. A causative role of wall stress in promoting t-tubule remodelling was established by applying stretch to papillary muscles ex vivo under culture conditions. Loads comparable to wall stress levels observed in vivo in the proximal zone reduced expression of junctophilin-2 and promoted t-tubule loss. CONCLUSION Elevated wall stress reduces junctophilin-2 expression and disrupts t-tubule integrity, Ca(2+) release, and contractile function. These findings provide new insight into the role of wall stress in promoting heart failure progression.
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Affiliation(s)
- Michael Frisk
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Marianne Ruud
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Emil K S Espe
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | | | - Åsmund T Røe
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Lili Zhang
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Per Andreas Norseng
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Ole M Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Geir A Christensen
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Ivar Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, 0424 Oslo, Norway K.G. Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
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Abstract
When poly(ethylene glycol) 3350 is estimated by the method of Skoog [(1979) Vox Sang. 37, 345-349], fine particles form. The particles are not attributable to residual protein but to a poly(ethylene glycol)/barium/iodine complex that can be quantitated by means of a laser nephelometer. The method is sensitive to at least 10 mg% poly(ethylene glycol) 3350 (4 micrograms in the cuvette) in 2500 mg% protein, and nephelometer response is approximately linear between 30 and 200 mg% of the polymer. The coefficient of variance is about 8%. Triton X-100, Pluronic F-68, Varonic 1000MS, and poly(ethylene glycol) of higher and lower molecular weight react well. Alkylated celluloses, dextrans, glycerol, glycine, and sodium dodecyl sulfate do not react significantly. Barium can be replaced with Mg, Ca, Ni, Fe, and other divalent cations in the reaction, but other than for Hg, light-scattering is most intense with Ba. The reaction goes to completion in about 5 min and is most intense when the barium is added before the iodine.
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