1. 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 31979 (24.8%)0.839±0.2252020 (51.3%)1.186±1.130 Cell#10,bottom 1167 (6.0%)0.710±0.2233118 (58.1%)1.044±0.474 Cell#8,top 12235 (28.7%)0.871±0.2731811 (61.1%)1.863±1.188 Cell#11,top &bottom combined 365118 (32.4%)0.888±0.3007443 (58.1%)1.255±0.831 Cell#13,bottom 15332 (20.9%)0.775±0.2764727 (57.5%)1.112±0.529 Cell#19,bottom 14921 (14.1%)0.719±0.2893920 (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

2. original cell#5_bottom 20  m 5*

3. cell#5_bottom Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

4. cell#5_bottom Results All peaks Nearest neighbors distance mean=1.186087 SD=1.1298 # peaks total39 # >1 mkm neighbor20 % >1 mkm neighbor51.28205 Nearest neighbors distance mean=0.8389 SD=0.224932 # peaks total319 # >1 mkm neighbor79 % >1 mkm neighbor24.76489 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)

5. original cell#10 bottom 20  m 10*

6. cell#10 bottom_part2 Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

7. cell#10 bottom_part2 Results Nearest neighbors distance mean=1.044465 SD=0.473462 # peaks total31 # >1 mkm neighbor18 % >1 mkm neighbor58.06452 Peak amplitude Nearest neighbor distance SD mm # of peaks Nearest neighbor distance Peak amplitude SD mm All peaks Nearest neighbors distance mean=0.709807 SD=0.22313 # peaks total116 # >1 mkm neighbor7 % >1 mkm neighbor6.034483 Peaks with higher amplitudes (> mean + 2 x SD)

8. original cell#8_top 20  m 8*

9. cell#8_top Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

10. Results cell#8_top Nearest neighbors distance mean=0.871316 SD=0.272693 # peaks total122 # >1 mkm neighbor35 % >1 mkm neighbor28.68852 Nearest neighbors distance mean=1.863152 SD=1.188314 # peaks total18 # >1 mkm neighbor11 % >1 mkm neighbor61.11111 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)

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

12. Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 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)

13. Nearest neighbors distance mean=0.90492 SD=0.277029 # peaks total179 # >1 mkm neighbor58 % >1 mkm neighbor32.40223 Nearest neighbors distance mean=1.272968 SD=0.925537 # peaks total43 # >1 mkm neighbor22 % >1 mkm neighbor51.16279 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)

14. original cell#11_top 20  m 11*

15. cell#11_top Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal original

16. cell#11_top Results Nearest neighbors distance mean=0.871494 SD=0.320551 # peaks total186 # >1 mkm neighbor60 % >1 mkm neighbor32.25806 Nearest neighbors distance mean=1.229789 SD=0.691429 # peaks total31 # >1 mkm neighbor21 % >1 mkm neighbor67.74194 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)

17. original cell#13_bottom 20  m 13*

18. cell#13_bottom Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

19. cell#13_bottom Results Nearest neighbors distance mean=0.7752 SD=0.275637 # peaks total153 # >1 mkm neighbor32 % >1 mkm neighbor20.91503 Nearest neighbors distance mean=1.122367 SD=0.528519 # peaks total47 # >1 mkm neighbor27 % >1 mkm neighbor57.44681 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)

20. originalcell#19_bottom 20  m 19*

21. cell#19_bottom Intensity peaks of RyR labeling identified by “SD-slicing” computer algorithm (color dots). -0.600.61.21.82.43.03.644.65.25.8 Peak amplitudes are coded by a rainbow-color scheme Units are SD of total cell signal Mean of total cell signal

22. cell#19_bottom Results Nearest neighbors distance mean=1.186087 SD=1.1298 # peaks total39 # >1 mkm neighbor20 % >1 mkm neighbor51.28205 Nearest neighbors distance mean=0.71933 SD=0.28924 # peaks total149 # >1 mkm neighbor21 % >1 mkm neighbor14.09396 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)