title: Prolonged mechanical unloading affects cardiomyocyte excitation-contraction coupling, transverse-tubule structure, and the cell surface.
abstract: Prolonged mechanical unloading (UN) of the heart is associated with detrimental changes to the structure and function of cardiomyocytes. The mechanisms underlying these changes are unknown. In this study, we report the influence of UN on excitation-contraction coupling, Ca(2+)-induced Ca(2+) release (CICR) in particular, and transverse (t)-tubule structure. UN was induced in male Lewis rat hearts by heterotopic abdominal heart transplantation. Left ventricular cardiomyocytes were isolated from the transplanted hearts after 4 wk and studied using whole-cell patch clamping, confocal microscopy, and scanning ion conductance microscopy (SICM). Recipient hearts were used as control (C). UN reduced the volume of cardiomyocytes by 56.5% compared with C (UN, n=90; C, n=59; P<0.001). The variance of time-to-peak of the Ca(2+) transients was significantly increased in unloaded cardiomyocytes (UN 227.4+/-24.9 ms(2), n=42 vs. C 157.8+/-18.0 ms(2), n=40; P<0.05). UN did not alter the action potential morphology or whole-cell L-type Ca(2+) current compared with C, but caused a significantly higher Ca(2+) spark frequency (UN 3.718+/-0.85 events/100 mum/s, n=47 vs. C 0.908+/-0.186 events/100 microm/s, n=45; P<0.05). Confocal studies showed irregular distribution of the t tubules (power of the normal t-tubule frequency: UN 8.13+/-1.12x10(5), n=57 vs. C 20.60+/- 3.174x10(5), n=56; P<0.001) and SICM studies revealed a profound disruption to the openings of the t tubules and the cell surface in unloaded cardiomyocytes. We show that UN leads to a functional uncoupling of the CICR process and identify disruption of the t-tubule-sarcoplasmic reticulum interaction as a possible mechanism.
authors.affiliation: Imperial College London, Harefield Heart Science Centre and Cardiovascular Sciences, London, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Ibrahim
authors.forename: Abeer
authors.initials: A
authors.lastname: Al Masri
authors.forename: Manoraj
authors.initials: M
authors.lastname: Navaratnarajah
authors.forename: Urszula
authors.initials: U
authors.lastname: Siedlecka
authors.forename: Gopal K
authors.initials: GK
authors.lastname: Soppa
authors.forename: Alexey
authors.initials: A
authors.lastname: Moshkov
authors.forename: Sara Abou
authors.initials: SA
authors.lastname: Al-Saud
authors.forename: Julia
authors.initials: J
authors.lastname: Gorelik
authors.forename: Magdi H
authors.initials: MH
authors.lastname: Yacoub
authors.forename: Cesare M N
authors.initials: CM
authors.lastname: Terracciano
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004594:Electrophysiology; D056966:Excitation Contraction Coupling / Q000502:physiology*; D008297:Male; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism*; D051381:Rats; D013314:Stress, Mechanical
chemical_list: D002118:Calcium