Mechanical unloading reverses transverse tubule remodelling and normalizes local Ca2+-induced Ca2+release in a rodent model of heart failure
- Michael Ibrahim1,
- Manoraj Navaratnarajah1,
- Urszula Siedlecka1,
- Christopher Rao1,
- Priyanthi Dias1,
- Alexey V. Moshkov2,
- Julia Gorelik2,
- Magdi H. Yacoub1 and
- Cesare M. Terracciano1,*
+ Author Affiliations
- 1Laboratory of Cell Electrophysiology, Harefield Heart Science Centre
- 2Laboratory of Functional Microscopy, Imperial College London, London, UK
- ↵*Corresponding author. Harefield Heart Science Centre, Imperial College London, London UB9 6JH, UK. Tel: +44 1895 453874, Fax: +44 1895 828 900, Email: firstname.lastname@example.org
- Received January 25, 2012.
- Revision requested February 28, 2012.
- Accepted March 2, 2012.
Aims Ca2+-induced Ca2+ release (CICR) is critical for contraction in cardiomyocytes. The transverse (t)-tubule system guarantees the proximity of the triggers for Ca2+ release [L-type Ca2+ channel, dihydropyridine receptors (DHPRs)] and the sarcoplasmic reticulum Ca2+ 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.
Methods and 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 Ca2+ 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 Ca2+ transient, an index of CICR dyssynchrony, was increased in HF and normalized by unloading. The increased Ca2+ 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.