Figure 8.

Effect of methyl p-hydroxybenzoate on the [Ca²⁺]_i of the human B-lymphoblastoid cell line GC-BB. In each experiment 0.5×10⁶ cells ml⁻¹ loaded with 5 μM fura-2/AM were added to the thermostated, magnetically stirred cuvette and the fluorescence ratio recorded. Once a steady resting [Ca²⁺]_i was reached, the effect of various agonists on calcium homeostasis was determined. (a) Where indicated, 4 mM methyl p-hydroxybenzoate were added. When [Ca²⁺]_i returned back to the resting level, 4-chloro-m-cresol and ionomycin were added. (b) Same as (a) except that 4-Cl-m-cresol was added prior to methyl p-hydroxybenzoate. Ionomycin was added at the end to determine the status of the intracellular stores. (c) Same as (a), but ionomycin was added first to deplete all intracellular calcium stores. Experiments were performed in Ca²⁺-free medium containing 0.5 mM EGTA. The traces are representative of at least five separate experiments.