InsP3R channel properties. (A) Dependence of normalized channel open probability Po on [InsP3] for WT, mH1-InsP3R3, mH4-InsP3R3, and D2590N-InsP3R3 channels, with optimum (2 μM) Ca2+ in pipette. Mean ± SEM, n = 4–8. (B) Mean channel open (τo) and closed (τc) times in response to Bcl-xL. (Upper) Channels activated with 1 μM InsP3 in presence of 2 μM Ca2+. Mean ± SEM, n = 4–14. (Lower Left) Kinetic effects of channel activation by 1 μM Bcl-xL in the presence of 1 μM InsP3 and 2 μM Ca2+. (Lower Right) Kinetic effects of channel inhibition by 10 μM Bcl-xL in presence of 3 μM InsP3 and 2 μM Ca2+. Mean ± SEM, n = 8–10. **P < 0.01. Related to Fig. 3.