the centers of RYRs and BK channel puncta. (When the nearest voxel distances between these channel puncta were considered, 9% of RYR2 puncta and 20% of RYR1 puncta were colocalized with BK channel puncta.) On average, the center of mass distance between RYR1s and their closest neighboring BK channel punctum was 296 ± 8.8 nm (n = 5 cells, 692 RYR1 puncta), and the center between RYR2s and their closest neighboring BK channel punctum was 340 ± 7 nm (n = 6 cells, 862 RYR2 puncta). A one-way ANOVA test indicated that BK channels localize further from RYR2s compared with RYR1s (P = 0.0006). The distribution of the center of mass distance between RYRs and BK channel puncta can be fitted with the probability distribution of distance to closest random point (Fig. 5 B). This fitting suggests that BK channel puncta randomly distribute inside the microdomain of Ca2+ sparks.
