The tightly regulated openings of the cardiac ryanodine receptor (RyR2) help to ensure that intracellular Ca2+- release from the sarcoplasmic reticulum (SR) can only occur when heart contractions are required. Usually this process is self-regulatory, where Ca2+ both activates and inhibits release of further Ca2+ from the SR. In the progression of heart failure some of this control is lost and in rest periods Ca2+ can leak from the SR into the cytosol. Recent evidence has suggested that Zn2+- dyshomeostasis may contribute to SR Ca2+- leak but the underlying mechanism is unclear. Using single channel electrophysiological studies in combination with live cell imaging of HEK 293 and fibroblasts, this study reveals that Zn2+, along with Ca2+ and the inhibitor Mg2+, plays a physiological role in the grading of Ca2+- release via RyR2. Importantly the data reveal that pathophysiological concentrations of Zn2+ (> 100pM) within the cytosol remove the requirement of Ca2+ to activate RyR2, resulting in irregular channel activity even in the presence of Mg2+. This increase in channel open probability due to Zn2+ is known to be associated with increased Ca2+- release events such as Ca2+ sparks suggesting that Zn2+ is a regulator of the SR Ca2+-leak current. A potential source of releasable Zn2+, which could modulate RyR2 activity in cardiomyocytes, are the acidic organelles (endosomes and lysosomes). This study provides key evidence that the two pore channels (TPCs), which are expressed on the surface of these organelles, are candidate channels for ligand-gated release of Zn2+. Importantly this research demonstrates that dysregulated Zn2+ homeostasis, resulting in elevated Zn2+ within the lysosome, has severe consequences upon cellular Ca2+- release from fibroblasts, which is primarily the result of Zn2+ acting as a pore blocker of TPC2. Together these data reveal a key role of Zn2+ as a second messenger which can regulate intracellular Ca2+- release in both health and disease.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:759346 |
| Date | January 2018 |
| Creators | Reilly-O'Donnell, Benedict |
| Contributors | Pitt, Samantha Jane |
| Publisher | University of St Andrews |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10023/16145 |
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