Panel A: Line graph showing time-course traces of cyto-iATP transients recorded from superior SA node regions. The horizontal axis represents time in milliseconds and the vertical axis represents normalized fluorescence intensity. Panel B: Line graph showing time-course traces of cyto-iATP transients recorded from inferior SA node regions. The horizontal axis represents time in milliseconds and the vertical axis represents normalized fluorescence intensity. Panel C: Scatter plot showing time to cyto-iATP peak for superior and inferior SA nodes. The horizontal axis represents SA node regions and the vertical axis represents time to peak in milliseconds. Panel D: Scatter plot showing cyto-iATP decay t 1/ 2 for superior and inferior SA nodes. The horizontal axis represents SA node regions and the vertical axis represents decay t 1/ 2 in milliseconds. Panel E: Scatter plot showing cyto-iATP transient duration for superior and inferior SA nodes. The horizontal axis represents SA node regions and the vertical axis represents transient duration in milliseconds.
Accelerated ATP decay and shorter transient duration characterize the high-flux phenotype of the superior SA node. (A and B) Representative time course traces of cyto-iATP transients recorded from superior (A) and inferior (B) SA node regions. Traces are normalized to peak amplitude to facilitate comparison of transient kinetics. The dashed line indicates baseline fluorescence (F/F0 = 1). (C–E) Summary quantification of cyto-iATP kinetic parameters (N = 5 mice per group), including time to peak (C), decay t1/2 (D), and total transient duration (E). P values are indicated in the text (time to peak, P = 0.2777; decay t1/2, P = 0.0181; duration, P = 0.0120). Large circles denote per-animal means; small circles indicate individual biological replicates. N represents the number of independent mice.