Fig. 4. Concentration-dependence of ATP-evoked endothelial Ca²⁺ signaling.

(A) Representative composite images of Ca²⁺ activity in carotid artery endothelium in response to stimulation with increasing concentrations of ATP. The three images show illustrative data from a single experiment in which the endothelium was stimulated with consecutively increasing concentration of ATP (from 100 nM to 10 mM). Scale bars, 50μm. (B) Average Ca²⁺ (F/F₀) responses from all cells in (A). The data shows responses to each concentration of the full series shown in A. The individual traces are color-coded based on the concentration of ATP applied (inset). (C) Ca²⁺ traces from a single cell. Color code is the same as shown in B. (D) Percentage of cells activated by increasing concentrations of ATP. The x-axis is log₁₀ of the CCh concentration. (E) Ca²⁺ traces corresponding to the datasets shown in A. Ca²⁺ signals from all 153 individual cells are shown. The color assigned to each trace is based on the amplitude of the initial response to ATP in each cell at the highest ATP concentration (right-most dataset), i.e. if a cell’s trace is colored blue in one set of traces, the same trace in the other data sets is also colored blue.