Fig. 10. High concentrations of tBid induce the PT and increase cytochrome c diffusibility in the intermembrane spaces. CyP-D(+) mitochondria were used and were saline-washed. All experiments were conducted with 1 µM buffered free Ca²⁺. Additions: 20 nM tBid, 100 nM tBid, 200 nM tBid and 1 µM CSA, as indicated. (A) Calcein-loaded mitochondria were incubated in SRM; other details as in Fig. 9A. Data are representative of three such experiments. (B) The two-step procedure was used to determine the diffusibility constant for cytochrome c. Means ± s.e.m. (four experiments).