SUPPLEMENT 2 This power point presentation reports analyses of RyR distribution measured by confocal microscopy in tangential sections of 6 SA node cells Summary of the analyses * Cell numbers are those assigned for 25 cells reported in Supplemental Figure 1 *Cell#, sectionAll peaks Peaks with higher amplitudes (> Mean+2 x SD)** Number of peaks #peaks with over-micron neighbors Nearest neighbor distance,  m Mean±SD Number of peaks #peaks with over-micron neighbors Nearest neighbor distance,  m Mean±SD Cell#5,bottom (24.8%)0.839± (51.3%)1.186±1.130 Cell#10,bottom 1167 (6.0%)0.710± (58.1%)1.044±0.474 Cell#8,top (28.7%)0.871± (61.1%)1.863±1.188 Cell#11,top &bottom combined (32.4%)0.888± (58.1%)1.255±0.831 Cell#13,bottom (20.9%)0.775± (57.5%)1.112±0.529 Cell#19,bottom (14.1%)0.719± (51.3%)1.186±1.130 Average ± SEM (21.2±4.0%)0.800±0.03 (56.2±1.6%)1.274±0.121 ** The SD in finding peaks with higher amplitude (>mean+2 x SD) was calculated for fluorescence peaks given in the units of the SD of the total fluorescence signal

original cell#5_bottom 20  m 5*

cell#5_bottom Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

cell#5_bottom Results All peaks Nearest neighbors distance mean= SD= # peaks total39 # >1 mkm neighbor20 % >1 mkm neighbor Nearest neighbors distance mean= SD= # peaks total319 # >1 mkm neighbor79 % >1 mkm neighbor Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm Peaks with higher amplitudes (> mean + 2 x SD)

original cell#10 bottom 20  m 10*

cell#10 bottom_part2 Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

cell#10 bottom_part2 Results Nearest neighbors distance mean= SD= # peaks total31 # >1 mkm neighbor18 % >1 mkm neighbor Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaks Nearest neighbors distance mean= SD= # peaks total116 # >1 mkm neighbor7 % >1 mkm neighbor Peaks with higher amplitudes (> mean + 2 x SD)

original cell#8_top 20  m 8*

cell#8_top Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

Results cell#8_top Nearest neighbors distance mean= SD= # peaks total122 # >1 mkm neighbor35 % >1 mkm neighbor Nearest neighbors distance mean= SD= # peaks total18 # >1 mkm neighbor11 % >1 mkm neighbor Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaksPeaks with higher amplitudes (> mean + 2 x SD)

original cell#11_bottom (main text Fig.8) 20  m 11*

Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal cell#11_bottom (main text Fig.8)

Nearest neighbors distance mean= SD= # peaks total179 # >1 mkm neighbor58 % >1 mkm neighbor Nearest neighbors distance mean= SD= # peaks total43 # >1 mkm neighbor22 % >1 mkm neighbor Results Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaks cell#11_bottom (main text Fig.8) Peaks with higher amplitudes (> mean + 2 x SD)

original cell#11_top 20  m 11*

cell#11_top Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal original

cell#11_top Results Nearest neighbors distance mean= SD= # peaks total186 # >1 mkm neighbor60 % >1 mkm neighbor Nearest neighbors distance mean= SD= # peaks total31 # >1 mkm neighbor21 % >1 mkm neighbor Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaksPeaks with higher amplitudes (> mean + 2 x SD)

original cell#13_bottom 20  m 13*

cell#13_bottom Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

cell#13_bottom Results Nearest neighbors distance mean= SD= # peaks total153 # >1 mkm neighbor32 % >1 mkm neighbor Nearest neighbors distance mean= SD= # peaks total47 # >1 mkm neighbor27 % >1 mkm neighbor Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaksPeaks with higher amplitudes (> mean + 2 x SD)

originalcell#19_bottom 20  m 19*

cell#19_bottom Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots) Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

cell#19_bottom Results Nearest neighbors distance mean= SD= # peaks total39 # >1 mkm neighbor20 % >1 mkm neighbor Nearest neighbors distance mean= SD= # peaks total149 # >1 mkm neighbor21 % >1 mkm neighbor Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaksPeaks with higher amplitudes (> mean + 2 x SD)