Effect of EGTA and tyrphostin on [Ca²⁺]_i mobilization induced by anti-B4–bR in Namalwa cells. (A) Anti-B4–bR induces both mobilization of intracellular Ca²⁺ and extracellular Ca²⁺ influx. Namalwa cells were pretreated with EGTA (0.5 mmol/L; Δ) at 60 seconds to chelate extracellular Ca²⁺ and were stimulated with the IT anti-B4–bR (5 nmol/L) at 125 seconds. CaCl₂ (0.5 mmol/L) was then added at 662 seconds to restore extracellular Ca²⁺. Response of control cells without pretreatment with EGTA, but with stimulation with IT and addition of Ca²⁺ are included (•). Data are expressed as HMFI versus time. (B) Dose-dependent effect of tyrphostin on [Ca²⁺]_i response induced by anti-B4–bR. Namalwa cells were pretreated for 18 hours at 37°C with increasing concentrations of tyrphostin (0 μmol/L; •); (10 μmol/L; □); (30 μmol/L; ▴); (50 μmol/L; ▵), (100 μmol/L; ▪), and (200 μmol/L; ○). Cells were then loaded with Fluo3-AM and analyzed by flow cytometry for IT-induced calcium mobilization. Data are expressed as HMFI versus time, and traces are representative of three experiments.