Response of U-87 cells to Bradykinin. (A) Superimposed line traces show the calcium increase upon exposure to different concentrations of bradykinin. The traces are the fluo4 ΔF/F vs. time for representative cells. (B) Dose-response relationships of bradykinin. Each value represents the average peak value of ΔF/F from 78-276 cells for each concentration tested. The average peak values for each concentration were fitted with sigmoidal dose-response and EC50 obtained was 6.7 nM of bradykinin. The maximum response was reached with 200 nM. (C) Typical Ca2+ response to repetitive application of ATP (10 μM). Line trace shows fluo4 ΔF/F vs. time for a representative cell. Note that the amplitude of the increase in [Ca2+]i in response to the second application ATP is significantly reduced as compared with the first application. (D). Typical Ca2+ response to ATP in a cell pre-treated with bradykinin (200 nM). Pre treatment with bradykinin did not results in any significant change in the response to fist exposure to ATP, however, the second response to ATP showed an increase in the amplitude as compared with untreated cells (C).