A high affinity blocker for inward-rectifier K+ channels, this compound is a stable derivative of the bee venom toxin tertiapin. Binds to ROMK1 (KIR1.1) and GIRK1/4 (KIR3.1/3.4) channels with high affinity (Ki values are 1.3 and 13.3 nM respectively) and is selective over IRK1 channels. Derivative tertiapin LQ (Cat. No. 4339) also available.