Desensitization of calcium transients in HMC-1 cells. Relative fluorescence was monitored from FURA-2–loaded cells before and during sequential addition of CXC chemokines at the times indicated by the arrows. The identity of each stimulus is indicated to the right of each arrow. The concentrations used were 10 ng/mL IL-8 and GRO and 25 ng/mL NAP-2 and ENA-78. Each tracing shown is from a single experiment and is representative of at least two separate experiments.