Fig. S4.

Early aftertransients (EATs) and early afterdepolarizations (EADs) in the NCX KO SAN. (A) Simultaneous recording of Ca fluorescence (Upper) and EGMs (Lower) using the same methods as Fig. S3, showing irregular spontaneous activity of an NCX KO SAN that exhibited frequent EATs (red arrows). Insets (Right) show expanded views of the simultaneous recordings. Inset 1 shows a normal Ca transient and depolarization whereas Inset 2 shows a Ca transient with an EAT. (B) Optical voltage recording of NCX KO SAN activity showing EADs (red arrows).