[Ca2+]i measurements in 106 A549 cells. 5 × 107 A549 cells were loaded with 2 μM indo-1/AM (see Materials and Methods), followed by washing and dual-wavelength measurement of fluorescence, using 106 cells/ml per measurement. [Ca2+]i was calculated as described. The three traces presented are representative for three independent experiments and show the effects of House dust mite extract (HDM), recombinant Der p 1 and recombinant Der p 5 on intracellular Ca2+ homeostasis. Arrows indicate when the compounds were added.