Fig. 4. (A) TMB-8 inhibits the IP₃-activated large conductance Ca²⁺ channel. Channel activity signals vesicle fusion (+100 mV clamp) (a). No spontaneous Ca²⁺ channels are observed after wash out (+45 mV clamp) (b). IP₃ activates a large conductance channel (41 pS) (+70 mV clamp) (c). TMB-8 (200 µM) inhibits channel activity (+60 mV clamp) (d). (B) Heparin inhibits the large conductance channel. Representative channel current recordings show Ca²⁺ channel activation in response to the application of IP₃ (+50 mV clamp) (a). The channels are inhibited by heparin (50 mV clamp) (b). (C) Dantrolene inhibits completely the large conductance channel. IP₃-activated Ca²⁺ channel (131 pS) (+80 mV clamp) (a). Inhibition by 100 µM dantrolene (+80 mV clamp) (b).