“…For the RyR2-only channels, we would expect a low maximum Po reflecting the fact that Ca 2+ , as a sole activator, is a partial agonist for RyR2 derived directly from cardiac tissue without purification (native channels; Ashley and Williams, 1990 ; Sitsapesan and Williams, 1994a ; Loaiza et al, 2013 ; Uehara et al, 2017 ). Similarly, considering RyR2 inactivation by cytosolic Ca 2+ , our results are in line with most of the published literature where RyR2 inhibition occurs at [Ca 2+ ] of 1 mM or lower ( Fruen et al, 1994 , 1996 ; Liu et al, 1998 ; Chamberlain et al, 1984 ; Meissner and Henderson, 1987 ; Zimányi and Pessah, 1991 ; Chu et al, 1993 ; Copello et al, 1997 ; Uehara et al, 2017 ; Wilson et al, 2021 ). Some groups find dissimilar results on maximum Po or RyR2 inactivation and these can be attributed to different methods of enrichment of RyR2, particularly where detergents have been used for purification ( Li and Chen, 2001 ; Xiao et al, 2007 ; Meli et al, 2011 ; Mukherjee et al, 2012 ).…”