Fig. 4. The source of the intracellular Ca²⁺ signal induced by testosterone. Cells were stimulated with testosterone in the presence of intracellular Ca²⁺ release inhibitors. (A) Pre-incubation of cells with nifedipine did not alter the Ca²⁺ response. (B) In Ca²⁺-free medium (0.5 mM EGTA) only the first peak was produced and no oscillations were observed. (C) Incubation with 1 mM Gd³⁺ (a nonspecific Ca²⁺ channel blocker) mimicked the response seen in Ca²⁺-free medium. (D) Ryanodine had no effect, whereas U73122 and 2APB abolished the Ca²⁺ signal (E,F).