FIG. 3.

LLO-pretreated cells exhibit diminished intracellular Ca²⁺ release but respond normally to ionophore-mediated Ca²⁺ influx. (A) Pretreated cells are refractory to LLO but not to ionomycin-mediated Ca²⁺ mobilization. BMMCs were pretreated (or not) with LLO (0.25 μg/ml) for 3 h, loaded with Indo 1-AM, and resuspended in Ca²⁺-containing medium. LLO was added to such cells at the time point indicated by the arrow marked “LLO,” and intracellular Ca²⁺ was measured. At the time point indicated by the other arrow, 1 μM ionomycin was added. (B) LLO-induced Ca²⁺ responses in pretreated cells under Ca²⁺-free conditions. BMMCs were incubated with (or without) LLO (0.25 μg/ml) for 4 h and then loaded with Indo 1-AM. To evaluate only the Ca²⁺ release from the intracellular stores, cells were thoroughly washed in Ca²⁺-free medium and then resuspended in Ca²⁺-free medium before stimulation with LLO (0.25 μg/ml) at the time point indicated by the arrow.