Transverse (t)-tubules are invaginations of the cell membrane vital for the synchronous rise of systolic calcium. In heart failure, t-tubules are lost leading to dys-synchronous calcium release. Nothing is known however, about the mechanisms that control atrial t-tubule formation or whether t-tubules can recover. Thus, this study aimed to investigate atrial t-tubule recovery following loss in heart failure, with emphasis on t-tubule density, calcium handling and proteins that contribute to t-tubule recovery. This study also aimed to gain understanding of how t-tubules form in the heart. Heart failure, and subsequent t-tubule loss, was induced in sheep by rapid ventricular pacing for ~ 36 days. Following 5 weeks of recovery, prompted by cessation of pacing, cardiac function, cellular hypertrophy and atrial tubule density all recovered. The organization of recovered tubules was altered however, with recovered tubules being predominately longitudinally orientated. Despite changes in orientation, recovered tubules were functional, in that, calcium was initially released along the tubules, followed by propagation to the rest of the cell. Recovery of atrial t-tubules was associated with increased expression of BIN1, Tcap and MTM1. Expressing these proteins in neonatal rat ventricular myocytes (NRVMs) demonstrated that BIN1 was sufficient to drive tubule formation, the structure of which was altered by coexpression with MTM1 and Tcap. Furthermore, NRVMs expressing variants 5, 8 and 9 of BIN1 exhibited increased systolic calcium transients and more synchronised calcium release. This is in contrast to skeletal muscle where tubule formation was dependent on the muscle specific variant 8 of BIN1. This study has shown that functional atrial t-tubules are restored following recovery from heart failure. The same proteins that were associated with t-tubule recovery were responsible for the formation of new tubule structures in the developing heart. This research identifies several targets, most notably BIN1, to facilitate t-tubule restoration and subsequent changes in calcium handling following loss in disease.
The control of formation and recovery of transverse tubules in the heart
Caldwell, J. (Author). 1 Aug 2020
Student thesis: Phd