Figure 2.

The negative chronotropic effect of ATP depends of P2 purinoceptors activation. The negative chronotropic effect of ATP (100 µM) was tested either in the absence or in the presence of the non-selective P2 receptor antagonist, PPADS (10 µM, B), the NTPDase inhibitor, POM-1 (100 µM, C), and the selective adenosine A₁ receptor antagonist, DPCPX (3 nM, D). The negative chronotropic effect of the enzymatically stable ATP analogue, ATPγS (100 µM, A), is also shown for comparison. Represented are box-and-whiskers plots, with whiskers ranging from minimum to maximum values calculated as a percentage (%) of variation from baseline; horizontal lines inside boxes indicate the corresponding medians. Each data point represents the result of a single experiment; data from the same experiment are connected by lines. *p < 0.05, ***p < 0.001 (Student’s t-test for paired samples) represent significant differences when compared to the effect of ATP alone.