title: Mechanical unloading reverses transverse tubule remodelling and normalizes local Ca(2+)-induced Ca(2+)release in a rodent model of heart failure.
abstract: OBJECTIVE
  Ca(2+)-induced Ca(2+) release (CICR) is critical for contraction in cardiomyocytes. The transverse (t)-tubule system guarantees the proximity of the triggers for Ca(2+) release [L-type Ca(2+) channel, dihydropyridine receptors (DHPRs)] and the sarcoplasmic reticulum Ca(2+) release channels [ryanodine receptors (RyRs)]. Transverse tubule disruption occurs early in heart failure (HF). Clinical studies of left ventricular assist devices in HF indicate that mechanical unloading induces reverse remodelling. We hypothesize that unloading of failing hearts normalizes t-tubule structure and improves CICR.
  
  
  RESULTS
  Heart failure was induced in Lewis rats by left coronary artery ligation for 12 weeks; sham-operated animals were used as controls. Failing hearts were mechanically unloaded for 4 weeks by heterotopic abdominal heart transplantation (HF-UN). HF reduced the t-tubule density measured by di-8-ANEPPS staining in isolated left ventricular myocytes, and this was reversed by unloading. The deterioration in the regularity of the t-tubule system in HF was also reversed in HF-UN. Scanning ion conductance microscopy showed the reappearance of normal surface striations in HF-UN. Electron microscopy revealed recovery of normal t-tubule microarchitecture in HF-UN. L-type Ca(2+) current density, measured using whole-cell patch clamping, was reduced in HF but unaffected by unloading. The variance of the time-to-peak of the Ca(2+) transient, an index of CICR dyssynchrony, was increased in HF and normalized by unloading. The increased Ca(2+) spark frequency observed in HF was reduced in HF-UN. These results could be explained by the recoupling of orphaned RyRs in HF, as indicated by immunofluorescence.
  
  
  CONCLUSIONS
  Our data show that mechanical unloading of the failing heart reverses the pathological remodelling of the t-tubule system and improves CICR.
authors.affiliation: Laboratory of Cell Electrophysiology, Harefield Heart Science Centre, Imperial College London, London, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Ibrahim
authors.forename: Manoraj
authors.initials: M
authors.lastname: Navaratnarajah
authors.forename: Urszula
authors.initials: U
authors.lastname: Siedlecka
authors.forename: Christopher
authors.initials: C
authors.lastname: Rao
authors.forename: Priyanthi
authors.initials: P
authors.lastname: Dias
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Moshkov
authors.forename: Julia
authors.initials: J
authors.lastname: Gorelik
authors.forename: Magdi H
authors.initials: MH
authors.lastname: Yacoub
authors.forename: Cesare M
authors.initials: CM
authors.lastname: Terracciano
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D020747:Calcium Channels, T-Type; D004195:Disease Models, Animal; D018450:Disease Progression; D006333:Heart Failure / Q000473:pathology*; D006353:Heart-Assist Devices; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000473:pathology*; D051381:Rats; D011917:Rats, Inbred Lew; D013318:Stroke Volume; D016277:Ventricular Function, Left; D020257:Ventricular Remodeling
chemical_list: D020747:Calcium Channels, T-Type