Sodium responses to ATP and UTP in immunolabeled chromaffin cells. A-C. Sodium images showing a group of chromaffin cells during stimulation with 100 μM ATP (B) and UTP (C) in presence of extracellular calcium. Panel A depicts cells prior to stimulation (control). Cells were allowed to rest for 30 min between consecutive stimulations. The SBFI fluorescence ratio F340/F380 was determined for each cell in a field on a pixel-by-pixel basis. Images were coded in pseudocolor to show differences in the F340/F380 ratio. The images corresponding to ATP and UTP stimulation (B and C) were captured ~30 s after challenges (response peaks); D. Pseudocolor image of PNMT/TH immunofluorescence ratio (labeling index) and corresponding scale. Intensely colored red and green cells are adrenergic and noradrenergic cells, respectively. Scale bar = 50 μm. E. Time course of changes in F340/F380 fluorescence ratio for an NA-cell (depicted by an arrow in A-D). The lines denote superfusions with ATP and UTP; F. Frequency distribution histograms of sodium responses to ATP. Changes in ΔR= F340/F380 were determined from the experiment depicted in A-B and 11 similar experiments (n = 749 cells). The first column in each histogram represents ATP-unresponsive cells (ΔR < 0.05). Leftmost histogram: AD-cells; rightmost histogram: NA-cells. A lognormal distribution function was fitted to each histogram, not taking into account unresponsive cells. The horizontal bars represent mean ΔR ± S.D.