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Fig. 5. Effects of the extracellular Ca2+ concentration on Ca2+-dependent degranulation. Mast cells were stimulated with PMA and A23187 at various extracellular Ca2+ concentrations. (A) Degranulation activity at 20 minutes after stimulation is plotted against extracellular Ca2+ concentration. Values are expressed as the percentage of total ß-hexosaminidase as shown in Fig. 3, but ß-hexosaminidase at [Ca2+]ex=0 was subtracted. Each point was obtained from four independent preparations of wild-type cells (
) and four independent knockdown clones (
) [mean±s.e.m. (n=4)]. (B) Degranulation activity is re-plotted against intracellular Ca2+ concentration, which was estimated from Ca2+ concentration at plateau phase after stimulation using Fura-2 as shown in the inset. (Inset) Timecourses of intracellular Ca2+ concentration in wild-type cells induced by PMA and A23187 at various extracellular Ca2+ concentrations, indicated on each line. Cells were stimulated at the time indicated by the arrow. Ca2+ concentration was converted from ratio values and shown as a second ordinate.
