Fig. 3. Quantitative summary of effects of NO donors on peristalsis (A) and representative effects on NO donors on the behaviour of whole colonies (B,C). (A) Histogram showing the change, relative to controls, in the amplitude of peristaltic contractions induced by the NO donors SIN-1 (amino-3-morpholinyl-1,2,3-oxadiazolium) and SNAP (S-nitroso-N-acetylpenicillamine). Note that the change is largely reversible after exposure of reduced preparations to 50 µmol l^-1 SIN-1. Statistical significance: ^*P<0.05 or ^**P<0.01 with the Mann-Whitney test. Note that 10 µmol l^-1 1-(1-naphthyl)piperazine (NP) reduced the increase in peristaltic force induced by 10 µmol l^-1 SNAP, but the difference was not significant (n.s., P>0.05). N=10 (1 µmol l^-1 SIN-1), 6 (10 µmol l^-1), 4 (50 µmol l^-1) and 8 (wash), 6 (SNAP) and 4 (SNAP + NP). (B) Injection of SIN-1 in the left half of an initially relaxed colony led to a contracted state relative to the control (right) half. Black line indicates the position of the axial canal. (C) Injection of SNAP in the left half of an initially contracted colony led to a relaxed state relative to the control half.