Fig. 2. Recordings of effects of NO (nitric oxide) donors on peristaltic contractions of reduced preparations of R. koellikeri. (A) Recording of a single preparation immersed in 40 ml of ASW and first exposed to 40 ml of solvent (ASW), then consecutively to 40 and 400 µl of 1 mmol l^-1 SIN-1 (amino-3-morpholinyl-1,2,3-oxadiazolium) chloride to obtain final bath concentrations of 1 and 10 µmol l^-1, respectively. Note the diversity of shape of traces reflecting the contribution of different contraction waves to peristaltic events. Note also the dose-dependent increase in contraction amplitudes and in wave synchrony after exposure to SIN-1 and the reversibility of this response after washing. (B) Effect of SNAP (S-nitroso-N-acetylpenicillamine) on contractions induced by field electrical stimulation. Stimulation trains of 6 monopolar pulses of 10 ms each at 5 V and 2 Hz were applied as shown at arrows. Note that the induced robust contractions were invariably followed by a sharp, transient drop of the ongoing peristaltic waves. Note also the reversible drop in amplitude and duration of the induced contraction in the presence of SNAP. µN, microNewton.