Here, we report the impact of redox potential on isolated cardiac ryanodine receptor (RyR2) channel activity and its response to physiological changes in luminal [Ca 2+ ]. Basal leak from the sarcoplasmic reticulum is required for normal Ca 2+ handling, but excess diastolic Ca 2+ leak attributed to oxidative stress is thought to lower the threshold of RyR2 for spontaneous sarcoplasmic reticulum Ca 2+ release, thus inducing arrhythmia in pathological situations. Therefore, we examined the RyR2 response to luminal [Ca 2+ ] under reducing or oxidising cytoplasmic redox conditions. Unexpectedly, as luminal [Ca 2+ ] increased from 0.1 to 1.5 mM, RyR2 activity declined when pretreated with cytoplasmic 1 mM DTT or buffered with GSH:GSSG to a normal reduced cytoplasmic redox potential (-220 mV). Conversely, with 20 μM cytoplasmic 4,4'-DTDP or buffering of the redox potential to an oxidising value (-180 mV), RyR2 activity increased with increasing luminal [Ca 2+ ]. The luminal redox potential was constant at -180 mV in each case. These responses to luminal [Ca 2+ ] were maintained with cytoplasmic 2 mM Na 2 ATP or 5 mM MgATP (1 mM free Mg 2+ ). Overall, the results suggest that the redox potential in the RyR2 junctional microdomain is normally more oxidised than that of the bulk cytoplasm.
Hanna, A. D., Lam, A., Thekkedam, C., Gallant, E. M., Beard, N. A., & Dulhunty, A. F. (2014). Cardiac ryanodine receptor activation by a high Ca 2+ store load is reversed in a reducing cytoplasmic redox environment. Journal of Cell Science, 127(20), 4531–4541. https://doi.org/10.1242/jcs.156760