mean STOC amplitudes varied by threefold, no statistically significant difference in decay rate was detected. Although the decay in the largest quartile was somewhat longer than the first three groups, it still fell within the range of the mean open time of BK channels reported in smooth muscle (Singer and Walsh, 1987; Tanaka et al., 1997; Harper et al., 2001; Lu et al., 2008; Yang et al., 2009). The results in Fig. 2 indicate that STOC decay reflects the closing rate constant of BK channels and thus is determined by the BK kinetics and not by residual [Ca2+] upon termination of Ca2+ sparks. This conclusion is supported by the STOC simulations based on the spatial relationship between RYRs and BK channels (see Fig. 7).
