Isolated guinea-pig ileum. Upper panels: Representative trace recordings showing the effects of acetylcholine (ACh, 1 μM) (A), dimethylphenylpiperazinium (DMPP, 10 μM) (B), irinotecan (100 μM) (C) or SN-38 (100 μM) (D) on the spontaneous contractile activity of longitudinal muscle preparations. Lower panels: Representative trace recordings showing the effects of physostigmine (0.01 – 0.1 μM) (E) or irinotecan (10 – 100 μM) (F) on the cholinergic twitch contractions evoked by transmural electrical stimulation of longitudinal muscle preparations (1 ms, 0.1 Hz), w=washing.