from the center of an RYR punctum would be activated at a Po of 1, and its Po decreases steeply as BK channels localize further away; this Po reaches almost zero when the distance is ∼600 nm. A count of the number of BK puncta within 600 nm of an RYR puncta revealed that ∼20% of RYR1 and RYR2 did not have an associated BK channel punctum, and <5% of RYRs had >10 BK channel puncta. On average, an RYR2 punctum had 1.7 ± 0.05 BK channel puncta within 600 nm, and an RYR1 punctum had 2.5 ± 0.1 BK channel puncta nearby (n = 5 cells for RYR1 and 6 cells for RYR2, P < 0.001 RYR1 vs. RYR2 with a one-way ANOVA).
