Fig. 6. Ca²⁺ signals induced by testosterone involve a pertussis toxin-sensitive G protein. (A) Cells were incubated for 20 minutes with 50 µM genistein, a tyrosine kinase inhibitor, and then stimulated with testosterone (100 nM). The use of genistein did not modify the Ca²⁺ increases produced by the hormone. (B) Cells were permeabilized with saponin, the saponin was removed to allow the membrane to reseal, and then cells were stimulated with testosterone (dashed line); using this treatment neuroblastoma cells maintained their capacity to respond to the hormone. Permeabilization in the presence of GDPßS (100 nM; solid line) blocked the testosterone-induced Ca²⁺ increases. (C) When cells were incubated with PTX (1 µg/ml) for 6 hours and then stimulated with testosterone, the Ca²⁺ increases were blocked. The time of addition of the hormone is indicated (arrows).