Fig. 4.

Effects of XE-991 on the NANC relaxant responses induced by EFS (2 or 13 Hz, 120 mA, 1 ms, pulse trains of 2 min) of U46619 (0.1 μM)-precontracted longitudinal muscle strips of the rat gastric fundus. (A) Representative tracings showing the effects of XE-991 (20 μM). The submaximal relaxation amplitudes induced by EFS (2 Hz) were expressed as percentages of a maximal amplitude parameter measured from the maximal U46619-induced contraction point reached before the addition of any test substance to the maximal papaverine (300 μM)-induced relaxation point reached at the end of each experiment (parameter indicated with a in the panel). Similarly, the submaximal AUCs (mm min) of the relaxant responses induced by EFS (13 Hz) were divided by this same maximal amplitude parameter (mm) and expressed as min. On the contrary, each maximal relaxation amplitude induced by EFS (13 Hz) was expressed as a percentage of its own maximal amplitude parameter, measured from the U46619-induced contraction point reached at the start of each EFS-induced relaxation to the maximal papaverine (300 μM)-induced relaxation point reached at the end of each experiment (parameters indicated with b and c in the panel, respectively). (B) Mean NANC relaxations evoked by 2 Hz (left graph) or 13 Hz EFS (middle and right graphs) observed in the absence (0 XE-991, time controls) or presence of XE-991 (10–50 μM). Relaxations were measured as peak amplitudes (left and middle graphs) or AUCs (right graph) and are expressed as percentages of control responses. Each point represents the mean ± s.e.m. of responses observed in eight (0, 10 and 20 μM XE-991) or nine (50 μM XE-991) strips. Significant differences between test and control responses: *P < 0.05, **P < 0.01,***P < 0.001.