Adenine nucleotides, but not adenosine, increase Ca2+influx from the extracellular space in human subcutaneous fibroblasts. In panel A, human subcutaneous fibroblasts were incubated with 1 mM ATP or ADP in control conditions and in Ca2+-free medium (plus EGTA, 100 μM). Each bar represents pooled from an n number of experiments. The vertical bars represent S.E.M.. *p < 0.05 represent significant differences compared with the effect of ATP or ADP alone. Panel B illustrates [Ca2+]i oscillations caused by 5’-(N-ethylcarboxamide) adenosine (NECA, 10 μM), an enzymatically stable non-selective adenosine receptor agonist, compared with the effect of bradykinin (BK, 30 μM) in fibroblasts of the human subcutaneous tissue (Bi). NECA (10 μM) and BK (30 μM) were applied cumulatively in sequence (Bii) and in the reverse mode (Biii). Panel C shows BK (30 μM)-induced [Ca2+]i oscillations in the absence and in the presence of a non-selective adenosine receptor antagonist, 8-phenyltheophylline (8-PT, 2.5 μM). Cells were pre-incubated with the cell-permeant fluorescent calcium indicator, Fluo-4 NW (2.5 μM, see Methods). Changes in fluorescence were detected using a microplate reader. [Ca2+]i transients were calibrated to the maximal calcium load produced by ionomycin (5 μM, 100% response). Black arrows indicate the time of drugs application. No changes in baseline fluorescence was observed after application of 8-PT (2.5 μM). Each point represents pooled data from an n number of experiments. The vertical bars represent S.E.M..